Experimental Method

Recycled WC powder with a Fisher particle size of 3.00～10.00 μm and normal WC powder with a Fisher particle size of 10.00～18.00 μm were mixed with Co powder or Ni powder with a loose packing density of 0.5～0.7g/cm3 to prepare mixtures of grades YJ1, YJ2, N309, etc. The mixtures were shaped, degummed, and then sintered in a domestically produced horizontal vacuum furnace and a low-pressure hot isostatic pressing furnace manufactured by a German specialized equipment company. The low-pressure hot isostatic pressing process is as follows: loading → vacuum pumping → heating → maintaining sintering temperature → charging argon and pressurizing → maintaining pressure and temperature → cooling and depressurizing → unloading. Electron microscopy was used for metallographic analysis, and the linear shrinkage and shrinkage rate of the samples during the sintering process were measured by the low-pressure hot isostatic pressing sintering furnace to analyze the densification process. The test alloys were made into D43×22 straight horseshoe bits for calibration tests in mining operations.

Experimental Results

Comparison of Properties

Between Low-Pressure Hot Isostatic Pressing Treatment of Recycled Material and Vacuum Sintering Treatment of Normal Material. The two types of tungsten carbide powders, recycled and normal, were processed using the same manufacturing process, undergoing vacuum sintering and low-pressure hot isostatic pressing treatment, respectively. The results are listed in Table 1.

As can be seen from Table 1, the porosity of the alloy treated with low-pressure hot isostatic pressing using recycled WC powder is even lower than that of the normal alloy, and its performance has been significantly improved, with an increase in the transverse rupture strength value; moreover, the elimination of type B pores ranging from 10 to 25 μm indicates the intrinsic relationship between the reduction in porosity and the increase in transverse rupture strength, while also confirming the capability of low-pressure hot isostatic pressing sintering to eliminate pores in recycled alloys.

Low-Pressure Hot Isostatic Pressing Alloy Linear Shrinkage Test

The linear shrinkage and shrinkage rate of the samples during the sintering process in the low-pressure hot isostatic pressing furnace were measured as shown in the attached figure. The alloy undergoes two stages: vacuum sintering and hot isostatic pressing. The macroscopic pores are eliminated during the vacuum sintering stage, and the microscopic pores are eliminated during the hot isostatic pressing stage to achieve the final densification level.

Comparison of On-site Rock Drilling Effects

The two types of tungsten carbide?powders, recycled and normal, were made into alloys of grades YJ1, YJ2, N309, etc., and calibration tests were conducted at the Taolin Lead-Zinc Mine. The results are listed in Table 2.

The rock drilling calibration indicates that high-quality mining carbide?can be produced from recycled WC powder through low-pressure hot isostatic pressing treatment, and their performance is comparable to that of mining carbide?made from normal tungsten carbide.

Result Analysis

Process Characteristics of Low-Pressure Hot Isostatic Pressing for Eliminating Pores in Recycled carbide

The densification of carbide?primarily occurs during sintering, where the plastic flow of the binder phase and the rearrangement of WC grains are driven by surface tension. However, under atmospheric or vacuum sintering, a certain amount of porosity always remains after shrinkage densification is complete; this is because when pores are sealed, the stress inside the pores reaches equilibrium with the surface tension of the pores. Additionally, due to the mixed composition of recycled materials and the presence of more harmful impurities, large pores and voids are easily formed during vacuum sintering, leading to issues such as low alloy density, low fracture strength, significant hardness variations, and severe contamination of the alloy. Applying a certain pressure can promote further flow of the binder phase and rearrangement of WC grains, thereby greatly reducing or even completely eliminating these pores or voids.

Study on the Densification Mechanism of Low-Pressure Hot Isostatic Pressing

The change curve of the linear shrinkage rate of recycled carbide?samples during low-pressure hot isostatic pressing sintering is shown in the attached figure. There are three peaks on the shrinkage rate curve: Peak A appears at a sintering temperature of 1200°C, which is solid-phase sintering. Due to the low yield point of the binder phase, plastic flow occurs under a small external force. The flow of the binder metal changes the contact situation between powder particles, causing the carbide?particles to move and come closer together. Peak B appears during the liquid-phase sintering process at 1340°C, where WC particle rearrangement, solution precipitation, and skeleton formation result in significant shrinkage of the sintered body, and macroscopic pores are eliminated during the vacuum sintering process of low-pressure hot isostatic pressing. Peak C appears at the beginning of the pressurization stage, where the rise in pressure eliminates the micro-pores in the product. However, with the extension of the pressure maintenance time, no new shrinkage peak appears in the product.

Conclusion

(1) The physical and mechanical properties of the recycled alloy treated by low-pressure hot isostatic pressing are superior to those of alloys manufactured by conventional processes, with a significant reduction in porosity and the elimination of type B pores.

(2) The recycled alloy treated by low-pressure hot isostatic pressing does not fall short of normal alloys in on-site rock drilling tests, and its wear resistance is even improved.

(3) The mechanism by which low-pressure hot isostatic pressing improves the performance of the alloy is mainly the elimination of large-sized pores and the reduction in porosity.

Spherical cast tungsten carbide powder is a new type of ultra-wear-resistant ceramic particle material. Compared with traditional tungsten carbide, spherical cast tungsten carbide has two significant advantages: first, it has a regular spherical appearance, good powder flowability, and wettability, which results in good integration with the surrounding tissue when added as particles, reducing the likelihood of stress concentration; second, the internal structure of the tungsten carbide particles is dense, with good toughness, fine grains, high hardness, and the coating has excellent wear resistance and is less likely to break under load. Due to its outstanding performance, spherical cast tungsten carbide powder is gradually replacing traditional tungsten carbide powder in the surface protection of components in mining machinery, oil machinery, construction industry, and foundries, significantly improving the wear resistance, corrosion resistance, and oxidation resistance of workpieces, and extending the service life of workpieces.

Introduction to the Methods of Spherical Cast Tungsten Carbide

Currently, the spherical cast tungsten carbide powders available in the market are mainly prepared by the following methods: induction remelting spheroidization, plasma remelting spheroidization, and plasma rotating electrode atomization.

The induction remelting spheroidization method involves heating the material in a reactor to the spheroidization temperature through induction heating, and the material moves forward slowly the vibration of the furnace tube. If the dispersion of the material is not well controlled, the molten droplets will grow due to collision and adhesion, making particle size control difficult. Moreover, during the operation, the powder must not come into contact with the reactor, otherwise it will affect the entire spheroidization process and cause material waste.

The plasma remelting spheroidization method uses casting tungsten carbide powder as the raw material and employs radiofrequency plasma flame to heat argon gas to a high temperature of 3000 to 10000 ℃, melting the casting tungsten carbide particles into a liquid state and directly quickly condensing them into spherical particles. This method can easily obtain fine-grained spherical tungsten carbide powder by controlling the particle size and composition of the raw material.

The plasma rotating electrode atomization method uses a tungsten carbide rod as the electrode, fixed within the rod material bin, and then subjected to plasma atomization under inert gas protection. The plasma arc melts the end face of the high-speed rotating rod, and under the action of centrifugal force, the molten droplets separate from the edge of the molten pool and solidify in the form of spherical particles. This technology avoids the difficulty of material dispersion at ultra-high temperatures during remelting spheroidization, and the obtained spherical tungsten carbide powder has a narrow particle size distribution range and is easy to control.

The following will study the chemical composition, micro-morphology, microstructure, microhardness, and other powder properties of spherical cast tungsten carbide powders prepared by different methods.

Chemical composition

The table above shows the chemical composition of spherical cast tungsten carbide powder samples prepared by different methods. It can be observed that the main components of the spherical cast tungsten carbide powder are W and C elements, and all contain trace amounts of Fe, V, Cr, and Nb elements. The ideal spherical cast tungsten carbide should be a eutectic of WC and W2C, with an eutectic temperature of 2525 ℃ and a carbon content of 3.840% (by mass) at the eutectic point. From the data in the table, it can be seen that the total carbon content of the spherical cast tungsten carbide prepared by the plasma rotating electrode atomization method has the smallest deviation from the theoretical eutectic carbon content, with the lowest free carbon content; the powder obtained by the induction remelting spheroidization method has the largest difference in total carbon content from the theoretical value, with a difference of 0.170% (by mass). This is due to the carbon content increase caused by the graphite tube heating method used in the induction remelting spheroidization process. In addition, by comparing samples 2#, 3#, and 4# with similar particle sizes, it can be determined that the powder prepared by the plasma rotating electrode atomization method has the relatively lowest impurity content. However, the impurity content of sample 1# prepared by the plasma rotating electrode atomization method is relatively high, which may be related to the quality of the cast tungsten carbide raw material rod. This suggests that, compared to other methods, the plasma rotating electrode atomization method can more accurately control the carbon content of spherical cast tungsten carbide powder, preventing overeutectic and hypoeutectic reactions caused by carburization and decarburization, and obtaining a nearly complete eutectic structure, which is crucial for improving the microstructure and properties of spherical cast tungsten carbide.

Microscopic morphology

The image above shows the microscopic morphology of spherical cast tungsten carbide powders prepared by different methods. It can be observed that the spherical cast tungsten carbide powders prepared by the three methods are all regular and smooth, nearly spherical in shape.

The image above shows the cross-sectional photos of spherical cast tungsten carbide powders prepared by different methods. As can be seen from (a) and (b), the spherical tungsten carbide powder particles prepared by the plasma rotating electrode atomization method are dense with almost no defects. However, as seen in (c) and (d), there are some obvious pores within the spherical tungsten carbide powder particles prepared by the plasma remelting spheroidization method and the induction remelting spheroidization method, resulting in some hollow powders. The main reason for this is that the crushed tungsten carbide powder material used in the above methods is likely to contain residual pores from the casting process. During the short plasma or induction heating process, the interior of the crushed tungsten carbide powder is difficult to completely melt, leading to some residual pores within the particles.

Microstructure

The image above shows the microstructure photos of spherical cast tungsten carbide powder particles after corrosion. It can be observed that the internal structure of the spherical tungsten carbide powder particles prepared by the three methods mainly consists of a typical fine acicular WC and W2C eutectic structure. Compared to the plasma remelting spheroidization method and the induction remelting spheroidization method, the spherical cast tungsten carbide powder prepared by the plasma rotating electrode atomization method has a denser eutectic structure. This is because, unlike the plasma remelting spheroidization method and the induction remelting spheroidization method, the plasma rotating electrode atomization method completely melts the cast tungsten carbide feedstock rod and then solidifies by being thrown out under the action of centrifugal force. During the crystallization of the molten cast tungsten carbide, the degree of undercooling is greater, nucleation is more rapid, and a larger number of crystal nuclei are generated, resulting in a finer and denser eutectic structure.

Microhardness

The table below shows the average microhardness of spherical cast tungsten carbide powders prepared by different methods. It can be seen that the microhardness of the spherical cast tungsten carbide powders prepared by the three methods is all above 2800 HV0.1, with the powder prepared by the plasma rotating electrode atomization method having the highest microhardness, reaching 3045 HV0.1. This is mainly due to the finer eutectic structure within the spherical cast tungsten carbide prepared by the plasma rotating electrode atomization method.

Other Physical Properties of spherical cast tungsten carbide

The table below shows the flowability and apparent density values of spherical cast tungsten carbide powders prepared by different methods. It can be seen that the powder prepared by the plasma rotating electrode atomization method has the worst flowability and the smallest apparent density; whereas the powder prepared by the induction remelting spheroidization method has the best flowability and the largest apparent density.

Conclusion

(1) The spherical cast tungsten carbide prepared by the plasma rotating electrode atomization method has the smallest deviation from the theoretical eutectic carbon content, the lowest free carbon content, and relatively low impurity content.

(2) The spherical tungsten carbide powder particles prepared by the plasma rotating electrode atomization method are dense with almost no defects, and the eutectic structure is finer. The spherical tungsten carbide powder particles prepared by the plasma remelting spheroidization method and the induction remelting spheroidization method both have some obvious pores, resulting in some hollow powders.

(3) The spherical cast tungsten carbide powders prepared by the three methods mainly consist of WC and W2C phases.

(4) The microhardness of the spherical cast tungsten carbide powders prepared by the three methods is all above 2800 HV0.1, with the powder prepared by the plasma rotating electrode atomization method having the highest microhardness, reaching 3045 HV0.1. The powder prepared by the induction remelting spheroidization method has the best flowability and the largest apparent density.

(1) To reduce the alloy’s sensitivity to sintering temperature fluctuations and carbon content changes, and to prevent the uneven growth of carbide grains;

(2) To change the phase composition of the alloy, thereby improving the structure and properties of the alloy.

This paper reviews the effects of adding rare earth elements, metals, and metal carbides to cemented carbides on their properties.

The Effect of Adding Rare Earth Elements on Carbide Properties

Rare earth elements are the 15 lanthanide elements with atomic numbers ranging from 57 to 71 in the third subgroup of the Mendeleev periodic table, plus scandium and yttrium, which have similar electronic structures and chemical properties, totaling 17 elements. Rare earths are known as the “treasure trove” of new materials and are a group of elements of particular concern to scientists worldwide, especially material experts. The following sections discuss the effects of adding rare earth elements on the hardness, bending strength, and grain size of cemented carbides.

1.1 Hardness

Whether the addition of rare earths has a significant effect on the hardness of the alloy is an issue of concern. The influence of yttrium and lanthanum on WC-TiC-Co cemented carbides is not significant, but different rare earth elements have different trends; however, the hardness of alloys with Nd or Ce added, regardless of the content, is slightly higher than that of the untreated alloys, with an average increase of 0.3 HRA units. For YG6 alloys, the addition of mixed rare earths results in a decrease in hardness to varying degrees when the content reaches 1%; for YT? alloys, the hardness remains largely unchanged or slightly increased with the addition of La or Y.

1.2 Bending Strength

Data shows that adding a certain amount of rare earth elements to the alloy can increase its bending strength. After the addition of rare earth oxides, the strength of the alloy is improved due to the dispersion strengthening of nickel by the rare earth oxides. When the content of rare earths is 1.2% to 1.6% of the binder metal content, the bending strength of the alloy reaches its maximum value; after adding mixed rare earth oxides equivalent to 0.25% to 1.00% of the binder mass fraction, the bending strength of the WC-8%Co alloy is improved to some extent. When the addition amount is 0.25% to 0.50%, the bending strength can be increased by 1.5%, but excessive addition of rare earths will lead to a decrease in bending strength.

1.3 Grain Size of Carbides

A large number of literature reports have been published on the effect of rare earths on the WC grain size in cemented carbides, but there is no unified conclusion to date. Regardless of the type of rare earth element added, the carbide grains in the alloy are finer than those without additives, and as the amount added increases, the refinement becomes more pronounced, and the grain size of the rare earth element-added alloy appears more uniform than that of the untreated alloy; studies have shown that the addition of trace rare earth elements does not affect the particle size of tungsten carbide and the binder phase.

Through extensive observation of the WC grain size and microstructure of WC-Co-TiC-TaC with rare earths and WC-Co with rare earths alloys, it is believed that the effect of rare earths on the WC grain size of cemented carbides is determined by two refinement effects and one growth effect. Table 1 shows the comparison of properties between rare earth alloys and alloys without rare earths.

2 The Effect of Adding Metals on the Properties of Cemented Carbides

Commonly used metal additives include chromium, molybdenum, tungsten, tantalum, niobium, copper, aluminum, and others. Except for copper and aluminum, all of these can form carbides. Therefore, the change in the carbon content of the alloy must be considered when adding these metals.

2.1 Adding Noble Metals

Sintered cemented carbide products with added noble metals such as Ru, Rh, Pd, and Re exhibit high wear resistance and corrosion resistance and can be used in corrosive and abrasive media. Noble metals do not form carbide phases and exist in the binder metal as solid solutions. Ru and Re cause the formation of a substructure in the binder phase of the cemented carbide. Alloying sintered cemented carbides with noble metals can increase the microhardness and elastic modulus of the binder phase, while also improving the bending strength, compressive strength limit, and yield point of the sintered cemented carbide as a whole.

2.2 Adding Copper

The addition of a small amount of copper to alloys used in mining can both increase the strength of the alloy and improve its impact toughness. Research results indicate that after adding a small amount of copper to the WC-13% Fe/Co/Ni alloy, the hardness of the alloy slightly decreases, but the bending strength is significantly improved. When the copper content is around 0.8%, the alloy exhibits the best performance. Moreover, copper also has the effect of refining and spheroidizing WC grains.

2.3 Adding Alkali Metals

Alkali metals can promote the growth of WC grains, but their effect is limited by other factors. For instance, in the presence of silicon, sodium actually refines the WC grains; whereas if sodium is present during the carbonization process, the WC grains will become finer. Adding industrial-grade Li?CO? with a purity of 98% to 99% to the alloy results in a cemented carbide with coarser average grains, clear and well-defined grain edges, and high bending strength.

2.4 Adding Aluminum

The effect of adding a small amount of Al on the properties and structure of the WC-13% Fe/Co/Ni cemented carbide shows that the addition of a small amount of aluminum can refine the WC grains. While the hardness of the alloy increases by 2 to 3 HRA, the bending strength of the alloy can be improved by 100 to 200 MPa. When the amount of Al added exceeds 0.8%, the bending strength of the alloy decreases, which is due to reasons such as the enrichment of martensite at the phase interface and the relative change in the amount of γ phase. Table 2 shows the effect of metal additives on the properties of the alloy.

This paper takes WC-12Co cemented carbide as the research object. Firstly, nano WC-Co composite powders were prepared by in-situ reduction carbonization reaction at different temperatures, and the composite powders were rapidly densified by discharge plasma sintering technology. The sintered blocks were systematically studied to analyze the effect of the in-situ reduction carbonization reaction temperature on the distribution characteristics of special crystal planes.

Experiment

The raw materials used in the experiment were carbon black, blue tungsten (purity 99.5wt.%, average particle size 50μm) and cobalt oxide (purity 98.5wt.%, average particle size 35μm). Carbon black, blue tungsten, and cobalt oxide were weighed according to the proportion for generating WC-12Co powder, and high-energy ball milling was carried out in a hard alloy ball mill jar with ethanol as the ball milling medium. The mixed powders were subjected to in-situ reduction carbonization reaction at 850°C, 900°C, and 1000°C in a vacuum environment, with a holding time of 1 hour. 2wt% of grain growth inhibitor was added to the composite powders prepared by in-situ reaction, and discharge plasma sintering densification was carried out. The sintering temperature was 1080°C, the holding time was 5 minutes, and the sintering pressure was 60MPa.

Material phase analysis was carried out on a Rigaku D/max-3c X-ray diffractometer with an acceleration voltage of 35kV and a current of 30mA, and a scanning rate of 2°/min. The micro-morphology of the powder was observed on a FEI-NovaNano SEM field emission scanning electron microscope.

Results and of Crystal Plane Distribution

Figure 1 shows the thermogravimetric (TG-DSC) curves of the nano WC-Co composite powder synthesized by in-situ reaction when heated to 1000°C at a heating rate of 10°C/min under Ar gas protection. From the change in the TG curve, it can be seen that as the temperature increases, the mass of the in-situ synthesized WC-Co composite powder decreases. When the temperature reaches 1000°C, the reaction ends, and the powder weight loss reaches nearly 6%. Throughout the heating process, the mass loss of the composite powder is divided into two stages: the first stage is from room temperature to 190°C, where there is a significant decrease in powder mass due to the ease of gas adsorption by nanoscale powders, and the gas desorbs and releases during the heating process, causing powder weight loss; the second stage is from 628°C to 1000°C, where the weight loss rate decreases from high to low. This is because the composite powder did not fully react during the low-temperature in-situ reduction carbonization reaction, and a secondary reaction occurred during the heating process, resulting in rapid weight loss of the powder.

Figure 2 shows the nanoscale WC-Co composite powder prepared by in-situ reduction carbonization reaction at 850°C. The powder particle size is mainly distributed between 30~120nm, with an average particle size of ~83.4nm. The particles have a good sphericity, and spherical or quasi-spherical powders exhibit good dispersibility and flowability, which can effectively avoid hard agglomeration of the powder. This is beneficial for the uniform dispersion of the powder in the sintering mold, thereby ensuring the uniformity and density of the sintered bulk structure. The composite powder prepared by the in-situ reduction carbonization reaction is subjected to rapid sintering densification in an SPS system to obtain nearly fully dense WC-Co cemented carbide blocks. XRD tests are conducted on the alloy specimens in the direction perpendicular to the sintering pressure and in the direction parallel to the sintering pressure. The relative integral intensities (i.e., integral area) of the diffraction peaks for each crystal plane in the VD (vertical to the sintering pressure) and PD (parallel to the sintering pressure) planes of the specimens are obtained through fitting calculations and compared with the relative intensities (integral area) of the diffraction peaks for each crystal plane in the PDF card (which represents the diffraction peak intensity distribution characteristics of traditional sintered cemented carbides), as shown in Table 1. The results indicate that the sintered WC-Co cemented carbide block specimens exhibit a significant characteristic of high anisotropic distribution for specific crystal planes.

Figure 3 shows the XRD patterns of the VD (vertical to the sintering pressure) and PD (parallel to the sintering pressure) planes of the specimens obtained by SPS sintering of the nanoscale WC-Co composite powder prepared by in-situ reaction at 850°C. From the figure, it can be observed that on the PD plane, the intensity of the (0001) plane peak is lower, while the intensity of the (10-10) plane peak is relatively higher. By fitting and calculating the integral area of each diffraction peak, the relative integral area of each crystal plane and the proportion of each crystal plane’s integral area in the total integral area are obtained, as shown in Figures 5 and 6.

From Figure 5, it can be seen that on the PD plane, the integral area of the (0001) plane accounts for only 10.72% of the total integral area, which is a decrease of 3.3% from the 14.02% in the PDF card (as shown in Figure 4). The proportion of the (10-10) plane reaches 35.73%, which is higher than the 31.87% in the PDF card, and the proportion of the (10-11) plane decreases to 21.76% compared to the 28.11% in the PDF card. Compared to conventional cemented carbide samples, in the PD direction of the composite powder sintered block prepared by in-situ reaction at 850°C, the distribution proportion of the main characteristic planes (0001) and (10-11) decreases, while the distribution proportion of (10-10) increases.

Discussion

On the VD direction of the sample, as shown in Figure 6, the proportion of the (0001) crystal plane has significantly increased to 40%, compared to the 14.02% in the PDF card, while the proportion of the (10-10) crystal plane has decreased to 11.68%, a reduction of 20.19% from the 31.87% in the PDF card. From the above analysis, it can be understood that in the sintered block of composite powder prepared by in-situ reaction at 850°C, there is an orientation distribution of characteristic crystal planes. In the direction perpendicular to the pressure, WC grains rotate, causing the (0001) plane to become perpendicular to the pressure direction, thereby reducing the interfacial energy between WC grains. The sintered block of low-temperature in-situ reaction synthesis powder exhibits an orientation distribution characteristic of WC grain characteristic crystal planes, which is believed to be due to the formation of WC grains through secondary reactions during sintering, with atoms preferentially aligning along the (0001) plane and the rotation of WC grains under sintering pressure causing the (0001) plane to tend towards being perpendicular to the pressure direction.

When the temperature is raised to 900°C for in-situ reaction, the prepared composite powder is mainly WC with only a small amount of carbon-deficient phase. When the temperature is raised to 1000°C for in-situ reaction, pure WC-Co composite powder can be obtained. Since the crystal plane distribution of the grains in the powder is isotropic, the crystal plane distribution of WC grains does not change during the subsequent sintering densification process at 900°C and 1000°C, and they still exhibit a randomly distributed isotropic characteristic.

Conclusion

1) The nanoscale WC-Co composite powder prepared by low-temperature in-situ reduction carbonization reaction at 850°C can be sintered into cemented carbide block materials with a highly oriented distribution characteristic of WC grain crystal planes using SPS. The sintered blocks of in-situ reaction powder at 900°C and 1000°C maintain an isotropic distribution of WC grain characteristic crystal planes.

2) In the WC-Co cemented carbide with highly oriented characteristic crystal planes, the basal plane (0001) occupies the largest area fraction in the direction perpendicular to the sintering pressure, reaching 40.0%; the prism plane (10-10) occupies the largest area fraction in the direction parallel to the pressure, reaching 35.7%.

3) The phase purity of the composite powder generated by the in-situ reaction plays an important role in the crystal plane orientation of the sintered block. When the main phase of the composite powder is WC, the crystal plane distribution of the sintered block does not exhibit oriented characteristics. However, when the main phase of the composite powder is the carbon-deficient phase, the crystal plane of the sintered block presents an oriented distribution characteristic.

Cemented carbide cutting tools are very common in cutting operations, and the correct selection of cutting tools is crucial for ensuring processing efficiency and quality. By familiarizing ourselves with the composition ratio of cutting tool materials, we can select the appropriate tools to meet different machining requirements. Therefore, Zhangzhiyuan has compiled a list of 10 main materials and their common proportions to help find the best cutting tools.

Carbon Tungsten Carbide

Tungsten carbide is a material used for manufacturing cutting tools and is the primary material due to its ultra-high hardness and wear resistance, allowing the tools to remain sharp during high-intensity cutting processes.

(1) 60% – 70% Tungsten Carbide

Used for cutting tools that require higher toughness and impact strength, suitable for processing softer or more ductile materials.

① Suitable for processing: aluminum alloys, copper alloys, plastics, low-carbon steel, medium-carbon steel, etc.

② Suitable conditions: rough machining tools, such as turning tools, milling cutters, and tools for heavy cutting.

③ Representative tools: Sandvik GC4030 turning blade, Kennametal KCP25 series milling blade, etc.

(2) 70% – 80% Tungsten Carbide

Used for multi-functional cutting tools, balancing hardness and toughness, suitable for a wide range of cutting applications.

① Suitable for processing: stainless steel, alloy steel, tool steel, cast iron, etc.

② Suitable conditions: medium machining tools, such as general turning tools, milling cutters, and drilling cutters.

③ Representative tools: Sandvik GC1125 series blade, Kennametal KCPK30 milling blade.

(3) 80% – 85% Tungsten Carbide

Used for cutting tools with high hardness and wear resistance, suitable for processing harder metal materials.

① Suitable for processing: hardened steel, high-strength alloy steel, tool steel, and heat-resistant alloys, etc.

② Suitable conditions: finishing tools, high-speed cutting tools, and tools for difficult-to-machine materials, such as precision turning tools and high-speed milling cutters.

(4) 85% – 90% Tungsten Carbide

Used for cutting tools that require extremely high hardness and wear resistance, suitable for high-intensity and high-speed cutting applications.

① Suitable for processing: hardened steel, superhard alloys, titanium alloys, and nickel-based alloys, and other high-strength materials.

② Suitable conditions: high-hardness cutting tools, such as high-speed cutting tools used in aerospace and automotive manufacturing, and finishing tools that require extremely high wear resistance.

(5) 90% – 95% Tungsten Carbide

Used for cutting tools with ultra-high hardness and extreme wear resistance, suitable for processing very hard materials.

① Suitable for processing: superhard alloys, hardened steel, hard cast iron, and other high-hardness materials.

② Suitable conditions: ultra-precision machining tools, high-precision cutting tools, especially suitable for applications that require extreme wear resistance, such as mold manufacturing and precision machining of hard materials.

Cobalt Powder

Cobalt powder is a binder used in cemented carbide cutting tools that provides toughness and impact resistance, commonly used to balance the hardness and wear resistance of the tools.

(1) 3% – 6% Cobalt Powder

Used for cutting tools that require higher hardness and wear resistance, typically applied in finishing and high-speed cutting.

① Suitable for processing: high-strength alloy steel, hardened steel, stainless steel, etc.

② Suitable conditions: finishing tools, high-speed cutting tools, such as high-speed milling cutters and turning tools.

(2) 6% – 10% Cobalt Powder

This is the most common proportion range, suitable for multi-purpose tools, balancing hardness, toughness, and wear resistance, applicable to a wide range of cutting applications.

① Suitable for processing: general steel, cast iron, stainless steel, heat-resistant alloys, etc.

② Suitable conditions: turning tools, milling cutters, and drilling cutters, particularly suitable for processing medium to high-strength materials.

(3) 10% – 15% Cobalt Powder

Used for cutting tools that require higher toughness and impact strength, suitable for rough machining and heavy cutting tasks.

① Suitable for processing: high-hardness alloy steel, large castings, heat-resistant alloys, and other hard materials.

② Suitable conditions: rough machining tools, such as heavy cutting milling cutters, turning tools, and drills, especially used under high impact and high stress conditions.

(4) 15% – 25% Cobalt Powder

Used in specific cases, such as cutting tools that require extremely high toughness and impact resistance, particularly suitable for tools used under extreme heavy-duty cutting conditions.

① Suitable for processing: high-strength alloy steel, superhard materials, and other materials that require extremely high toughness and impact resistance.

② Suitable conditions: tools for rough machining, milling cutters with large cutting depths, turning tools, and cutting tools used under heavy-duty conditions.

Titanium Aluminum Carbide

Titanium aluminum carbide is a compound formed by titanium, aluminum, and carbon elements, commonly used as a coating or blended material for cemented carbide cutting tools to enhance hardness, wear resistance, and oxidation resistance.

(1) Ti-Al-C Ratio 1:1:1

This ratio of titanium aluminum carbide is typically used for high-temperature resistant coatings and structural materials, offering excellent high-temperature stability and hardness, suitable for cutting processes in high-temperature environments.

① Suitable for processing: high-temperature alloys, heat-resistant steels, stainless steels, and other materials.

② Suitable conditions: tools that require high-temperature and wear resistance, such as high-speed cutting tools, drills, and milling cutters.

(2) Ti-Al-C Ratio 2:1:1

With a higher titanium content in this ratio, the material’s toughness and oxidation resistance are enhanced, making it suitable for high-speed cutting and the processing of medium-strength materials.

① Suitable for processing: stainless steels, titanium alloys, heat-resistant alloys, etc.

② Suitable conditions: multi-purpose tools, such as turning tools, milling cutters, and drilling cutters, particularly suitable for processing medium-strength materials.

(3) Ti-Al-C Ratio 3:1:2

This ratio increases the proportion of aluminum, improving the material’s high-temperature and corrosion resistance performance, making it suitable for applications that require high oxidation resistance.

① Suitable for processing: ultra-high-temperature alloys, difficult-to-machine materials, corrosion-resistant alloys, etc.

② Suitable conditions: cutting tools used under extreme conditions, such as cutting tools for the aerospace industry and tools for processing high-temperature alloys.

Nickel Powder

Nickel powder is a binder material commonly used in cemented carbide cutting tools that enhances the toughness and corrosion resistance of the tools, particularly suitable for use in environments with high processing requirements.

(1) Nickel Content 10% – 15%

This proportion of nickel powder is used to improve the corrosion resistance and toughness of cutting tools, suitable for processing non-ferrous metals and corrosion-resistant materials.

① Suitable for processing: aluminum alloys, copper alloys, stainless steels, and other materials.

② Suitable conditions: tools for precision machining and those that require high corrosion resistance, such as milling cutters and drills.

(2) Nickel Content 15% – 20%

At this ratio, the higher nickel content enhances the tool’s impact resistance and toughness, suitable for heavy-duty machining and cutting of difficult-to-machine materials.

① Suitable for processing: heat-resistant alloys, high-strength steels, stainless steels, etc.

② Suitable conditions: tools for heavy cutting and rough machining, suitable for processing under high-stress conditions.

(3) Nickel Content 20% – 25%

This proportion of nickel powder is used for tools that require extremely high toughness and durability, suitable for high-intensity machining under extreme conditions.

① Suitable for processing: ultra-high-strength alloys, difficult-to-machine materials, and materials that require fatigue resistance.

② Suitable conditions: high-precision tools and heavy-duty machining tools, applicable in fields such as aerospace and nuclear industries.

Trace Elements

Titanium

Titanium is a lightweight, high-strength metal material with excellent corrosion resistance and biocompatibility. It is commonly used in the coatings and substrates of cemented carbide cutting tools to enhance the tool’s strength, wear resistance, and oxidation resistance.

(1) Titanium Content 10% – 15%

This proportion of titanium is used to enhance the wear resistance and strength of cutting tools, particularly suitable for use under high-temperature and high-stress conditions.

① Suitable for processing: stainless steels, titanium alloys, high-temperature alloys, and other materials.

② Suitable conditions: high-precision tools, high-temperature cutting tools, such as coated tools and milling cutters.

(2) Titanium Content 15% – 20%

At this ratio, the higher content of titanium is suitable for processing environments that require high strength and impact resistance.

① Suitable for processing: high-strength steels, nickel-based alloys, corrosion-resistant alloys, etc.

② Suitable conditions: heavy-duty machining tools, high-temperature resistant tools, particularly suitable for cutting applications in the aerospace and energy fields.

(3) Titanium Content 20% – 25%

This high proportion of titanium is mainly used to enhance the stability and durability of tools under extreme machining conditions, suitable for cutting difficult-to-machine materials.

① Suitable for processing: ultra-high-temperature alloys, difficult-to-machine metals, composite materials, etc.

② Suitable conditions: cutting tools used in extreme environments, such as tools for the nuclear industry, aerospace, and military applications.

Tantalum

Tantalum is a rare metal with a high melting point and good thermal conductivity, commonly used in the coatings and alloy compositions of cemented carbide cutting tools to enhance the tool’s wear resistance, heat resistance, and corrosion resistance, especially suitable for high-temperature and heavy-duty cutting environments.

(1) Tantalum Content 5% – 10%

This proportion of tantalum is used to enhance the wear resistance and thermal stability of cutting tools, suitable for cutting processes under medium to high temperatures.

① Suitable for processing: stainless steels, alloy steels, titanium alloys, etc.

② Suitable conditions: medium to high-temperature cutting tools, such as coated tools and milling cutters, applicable in industries like aerospace, automotive manufacturing, etc.

③ Representative tools: Iscar IC5500 series blades, Kennametal KCU15 blade.

(2) Tantalum Content 10% – 15%

At this ratio, the moderate content of tantalum further improves the tool’s corrosion resistance and oxidation resistance, suitable for use at even higher temperatures.

① Suitable for processing: high-temperature alloys, corrosion-resistant steels, stainless steels, etc.

② Suitable conditions: coated tools for extreme conditions, high-strength turning tools, particularly suitable for the energy and aviation fields.

③ Representative tools: Walter WKP35 series blades, Sandvik GC4225 blade.

(3) Tantalum Content 15% – 20%

This high proportion of tantalum is used for extreme high-temperature and heavy-duty cutting applications, ensuring that the tools maintain high performance under harsh processing conditions.

① Suitable for processing: ultra-high-temperature alloys, difficult-to-machine metals, wear-resistant materials.

② Suitable conditions: high-temperature coated tools for the nuclear industry and aerospace fields, heavy-duty milling cutters for extreme machining conditions.

Chromium

Chromium is a hard metal with good corrosion resistance and wear resistance, commonly used in the coatings and alloys of cemented carbide cutting tools to enhance the tool’s wear resistance, corrosion resistance, and oxidation resistance, particularly suitable for use under severe processing conditions.

(1) Chromium Content 5% – 10%

This proportion of chromium is used to enhance the tool’s wear resistance and corrosion resistance, suitable for moderate-intensity cutting applications.

① Suitable for processing: stainless steels, alloy steels, cast irons, etc.

② Suitable conditions: cutting tools with moderate strength, such as general turning tools and milling cutters.

(2) Chromium Content 10% – 15%

At this ratio, the increased content of chromium improves the tool’s oxidation resistance and durability, suitable for higher temperature and more severe processing environments.

① Suitable for processing: high-temperature alloys, corrosion-resistant steels, nickel-based alloys, etc.

② Suitable conditions: high-temperature cutting tools, corrosion-resistant coated tools, applicable in aerospace and energy fields.

(3) Chromium Content 15% – 20%

This high proportion of chromium is used for tools that require extremely high wear resistance and corrosion resistance, especially for processing at extreme temperatures.

① Suitable for processing: ultra-high-temperature alloys, corrosion-resistant alloys, hard metals, etc.

② Suitable conditions: high-temperature coated tools for the nuclear industry and aerospace fields, heavy-duty cutting tools for extreme conditions.

Niobium

Niobium is a rare metal with a high melting point, excellent heat resistance, and corrosion resistance. It is commonly used in the coatings of cemented carbide cutting tools or added as an alloying element to enhance the tool’s stability and oxidation resistance during high-temperature and high-intensity processing.

(1) Niobium Content 5% – 10%

This proportion of niobium is used to enhance the tool’s thermal stability and oxidation resistance, suitable for cutting operations under medium to high temperatures.

① Suitable for processing: stainless steels, titanium alloys, nickel-based alloys, etc.

② Suitable conditions: high-temperature cutting tools and corrosion-resistant coated tools, such as turning and milling cutters.

(2) Niobium Content 10% – 15%

At this ratio, the increased content of niobium significantly enhances the tool’s high-temperature strength and fatigue resistance, suitable for use under extreme processing conditions.

① Suitable for processing: high-temperature alloys, corrosion-resistant steels, stainless steels, etc.

② Suitable conditions: high-strength turning tools, heavy-duty milling cutters, especially suitable for high-demand fields such as aerospace and nuclear industries.

(3) Niobium Content 15% – 20%

This high proportion of niobium is used for tools that require extremely high heat resistance and oxidation resistance, particularly suitable for use in ultra-high temperatures and extreme processing conditions.

① Suitable for processing: ultra-high-temperature alloys, corrosion-resistant alloys, composite materials, etc.

② Suitable conditions: high-temperature coated tools under extreme environments, high-precision cutting tools, especially applicable in nuclear and aerospace industries.

Vanadium

Vanadium is a metal element used to enhance the wear resistance and oxidation resistance of cutting tools. It is commonly added as an alloying additive or coating material to cemented carbide cutting tools to improve their performance during high-temperature and high-intensity processing.

(1) Vanadium Content 5% – 10%

This proportion of vanadium is used to enhance the tool’s wear resistance and oxidation resistance, suitable for cutting operations under medium to high temperatures.

① Suitable for processing: alloy steels, stainless steels, high-temperature alloys, etc.

② Suitable conditions: for turning and milling cutters, especially for high-temperature cutting and applications requiring high corrosion resistance.

(2) Vanadium Content 10% – 15%

At this ratio, the increased content of vanadium further improves the tool’s high-temperature strength and wear resistance, suitable for processing under extreme conditions.

① Suitable for processing: high-strength steels, corrosion-resistant alloys, nickel-based alloys, etc.

② Suitable conditions: for heavy-duty turning tools, milling cutters, especially for cutting under high-temperature and high-stress conditions.

(3) Vanadium Content 15% – 20%

This high proportion of vanadium is used for tools that require extremely high wear resistance and oxidation resistance, particularly suitable for use in ultra-high temperatures and extreme processing conditions.

① Suitable for processing: ultra-high-temperature alloys, corrosion-resistant materials, composite materials, etc.

② Suitable conditions: for high-temperature coated tools under extreme environments, high-precision cutting tools, especially applicable in aerospace and energy fields.

Titanium Carbide of Cutting tools

Titanium carbide is an ultra-hard material commonly used as a coating or as an alloy component in cemented carbide cutting tools. It significantly improves the tool’s hardness, wear resistance, and high-temperature performance, making it suitable for cutting operations in high-intensity and high-temperature environments.

(1) Titanium Carbide Content 10% – 15%

This proportion of titanium carbide is used to enhance the tool’s wear resistance and thermal resistance, suitable for cutting at high temperatures.

① Suitable for processing: stainless steels, alloy steels, titanium alloys, etc.

② Suitable conditions: for high-speed milling and turning tools, especially in cases where high wear resistance is required.

③ Representative tools: Sandvik GC1125 series blades, Walter WKK10 series blades.

(2) Titanium Carbide Content 15% – 20%

At this ratio, the content of titanium carbide is further increased, significantly improving the tool’s hardness and wear resistance, suitable for processing under extreme conditions.

① Suitable for processing: high-temperature alloys, hard metals, nickel-based alloys, etc.

② Suitable conditions: for heavy-duty cutting tools, precision milling cutters, especially for processing under high-temperature and high-stress conditions.

(3) Titanium Carbide Content 20% – 25%

This high proportion of titanium carbide is used for tools that require extremely high hardness and heat resistance, particularly suitable for use in extreme high-temperature and heavy-duty processing conditions.

① Suitable for processing: ultra-high-temperature alloys, composite materials, corrosion-resistant materials, etc.

② Suitable conditions: for high-temperature coated tools in aerospace, nuclear industry, and other fields, as well as high-precision cutting tools.

Gaining a deep understanding of the proportions of tool materials and making the optimal choice using a rational and scientific approach inherently reflects the scientific spirit of cutting machining professionals. The scientific spirit is not only about the thirst for knowledge and rigor in details, but also about the dedication to technological research and the pursuit of precision. Upholding the scientific spirit, cutting machining professionals continuously drive the progress of the manufacturing industry.What are the important proportions of cemented carbide materials?

Typically, nano-WC powders are prepared using gas-phase reaction methods or high-energy ball milling techniques. The most widely used method for preparing WC-Co composite powders is through hydrogen reduction/carbonization of tungsten oxide. Therefore, controlling the microstructure and preparation process of tungsten oxide can yield nano-tungsten powder. However, there is currently a lack of in-depth research on how different carbonization methods affect the carbonization process of nano-tungsten powder. Research in this area holds significant practical value for the production of nano-tungsten carbide powders and the fabrication of nano-crystalline WC-Co carbides.

This study uses ball-milled tungsten oxide as the raw material and prepares nano-tungsten powder by controlling the hydrogen reduction process. Different carbonization methods, namely wet ball milling and dry milling, are employed to mix carbon, resulting in W+C mixed powders with varying morphologies. After carbonization, WC powder is obtained, aiming to enhance the uniformity of the dispersion of tungsten and carbon black particles through suitable carbonization methods and to explore a cost-effective industrial method for preparing homogeneous nano-WC powder.

The Importance of Carbon Content in Carbide?Powders

Carbon content is a crucial factor influencing the performance of carbides. Even minor fluctuations in carbon content can lead to changes in the alloy’s phase composition and microstructure, thus affecting its performance. When the carbon content in an alloy is insufficient, decarburized phases, which are brittle and unstable, may form, resulting in reduced strength and increased susceptibility to fracture and chipping during use. Conversely, when carbon content is too high, free graphite may form within the alloy, disrupting the continuity of the matrix and adversely affecting properties such as bending strength, toughness, and wear resistance.

Even fluctuations in carbon content within the normal phase range can significantly impact alloy performance. At the upper limit, strength and toughness are high while hardness and coercivity are low; at the lower limit, the opposite is true. This is because changes in carbon content, while not altering the number of phases, do modify the composition of the bonding phase. The hardness of the bonding phase is determined by tungsten content, which can be controlled by the total carbon in the raw materials during the sintering process. Thus, the overall carbon content of the alloy is vital for the material’s hardness and toughness. Studies of high-lifetime micro-drills and stamping dies have shown that the saturation magnetization of long-lasting alloys is typically controlled within 75% to 80%, indicating that their carbon content is maintained at the lower limit of the normal phase range.

Experimental Method

To further improve the uniformity of the powder and reduce particle agglomeration, mechanical milling and classification were used to preprocess WO. The preprocessed powder (MWO?) was then subjected to hydrogen reduction in a tubular furnace at 760°C to obtain nano-W powder. Following this, an appropriate dispersant was added for wet mechanical alloying and carbon mixing. After vacuum drying, the mixture was carbonized in a hydrogen molybdenum wire furnace at 1140°C, followed by crushing to obtain nano-WC powder. Additionally, dry milling was also employed for carbon mixing under the same carbonization conditions for comparative analysis. Scanning electron microscopy (SEM) was used to observe the morphology of WO?, W, and WC powders, while powder properties such as particle size, specific surface area, and total carbon content were measured. Specific surface area and particle size of the nano-W powder were measured using a SA3100 specific surface area analyzer and a particle size analyzer, and the morphology and uniformity of the powder were examined with a QUANTA-200 SEM.

Results and Discussion of the Experiment

Morphology and Properties of Nano-WC Powder

Figure 1 shows SEM images of the raw powder and nano-W powder. The results indicate that mechanical milling significantly refines the WO? powder, achieving a particle size of 1.1 μm and a specific surface area of 4.52 m2/g. After mechanical nano-sizing, the morphology of the WO? powder changed significantly, with smooth surfaces and a dense structure consisting of nano-particles. The large agglomerated WO? particles were crushed into finer particles with maximum agglomerates not exceeding 20 μm. Using MWO as a raw material under specific processing conditions, nano-sized W powder (20-30 nm) was produced, exhibiting inherited structural characteristics from its oxide precursor and showing varying degrees of loose agglomeration, with maximum agglomerate sizes not exceeding 20 μm.

Morphology of W+C Mixture after Carbon Mixing

Figure 2 presents SEM images of the W+C mixtures obtained through different methods. After wet mechanical alloying with an appropriate dispersant, significant changes in the powder morphology were observed: most agglomerated W particles were effectively broken up and dispersed, with carbon black uniformly distributed. In contrast, the dry milling method resulted in noticeable agglomeration of W powder, with non-uniform distribution of carbon black.

Morphology and Structure of Nano-WC Powder

Figure 3 shows SEM images of different nano-WC powders. The nano-WC powder obtained through wet alloying with carbon was smaller and more uniform, with a well-defined morphology and minimal agglomeration, containing a total carbon content of 6.10-6.30%, a combined carbon content of 6.06%, and an average particle size of about 85 nm. In contrast, the WC powder produced through dry milling exhibited more tightly bound agglomerates and larger particle sizes, with an average size of approximately 189 nm. This discrepancy is attributed to the insufficient breaking of tungsten powder agglomerates during carbon mixing in the latter method, resulting in poor contact between carbon black and tungsten powder and non-uniform carbon distribution. During high-temperature solid-state reactions, the chemical migration process is lengthy and requires significant chemical driving force, making complete carbonization challenging; high temperatures can also cause tungsten particles within agglomerates to grow larger due to sintering.

Conclusion

1.Using wet mechanical alloying for carbon mixing followed by carbonization at 1140°C, a well-dispersed and uniform nano-WC powder was produced, with a total carbon content of 6.10-6.30% (controllable), a combined carbon content of 6.06%, and an average particle size of approximately 85 nm.

2.The use of wet milling for carbon mixing altered the agglomerated appearance of the nano-tungsten particles, improving the uniformity of the dispersion of W and C powders. This approach facilitates lower carbonization temperatures and results in uniformly sized and chemically stable nano-WC powders.

Erosion-Wear Experimental Materials and Equipment

Experimental Materials

Tungsten carbide (WC) carbide?is a composite material produced using powder metallurgy techniques, with WC, a metal carbide that is difficult to dissolve, as the matrix and a binder added. It is characterized by high hardness and strong wear resistance. The WC carbide?used in this experiment is YG8, which is employed as the coating material for the valve core and outlet sleeve in coal direct liquefaction devices. YG8 is a tungsten-cobalt carbide?with a cobalt binder, a density of 14.6 g/cm3, a hardness of HV 1350, an elastic modulus of 540 MPa, a bending strength of 1500 MPa, and a compressive strength of 4470 MPa.

The experiment uses quartz sand (SiO?) particles as the erosion particles, which are commonly used in erosion-wear tests. The particles are sieved to achieve an average particle size of 150 μm, as shown in Figure 1.

Experimental Equipment

The experiment uses a self-made shock wave-driven gas-solid two-phase flow erosion-wear testing device. This device primarily consists of a shock wave generator, a velocity measurement system, a high-speed camera, a heating system, and a temperature control system.

In this setup, nitrogen gas is connected to the driving section to generate shock waves with a specific Mach number. The driving section and the driven section are separated by an aluminum film. Experimental particles are placed on a tin foil located between the driven section and the accelerating section. By adjusting the pressure relief valve, gas is introduced into the driving section of the shock tube. When the pressure difference across the film reaches a critical value, the film ruptures suddenly, generating a shock wave. The high-speed gas flow then propels the solid particles through the accelerating section to the desired experimental velocity. Upon impacting the specimen surface, the high-speed particles cause material loss, thus facilitating the erosion process.

The driving section, driven section, and accelerating section are each equipped with dynamic pressure sensors, charge amplifiers, and dynamic test analyzers to measure shock wave velocity. A high-speed camera in the experimental section captures the particle motion trajectories. The specimen holder is equipped with a temperature heating system and a temperature control system, allowing for adjustment to the required experimental temperature.

Erosion-Wear Experimental Parameters and Methods

Experimental Parameters

The impact angle, denoted as θ (see Figure 3), is defined as the angle between the axis of the shock tube and the surface of the specimen being eroded (0°to 90°). The desired impact angle is achieved by rotating the specimen holder.

The impact distance L is the distance between the center of the shock tube’s outlet and the center of the specimen’s surface. Typically, L is set between 30 and 50 mm during experiments. When conducting experiments at different impact angles, the position of the shock tube needs to be adjusted to maintain a consistent impact distance.

In the experiment, the impact velocity is adjusted by changing the thickness of the aluminum foil. Aluminum foils with thicknesses of 0.13 mm, 0.20 mm, and 0.30 mm are used for the erosion-wear tests. A high-speed camera is employed to record the particle trajectories. By analyzing these trajectories, the particle velocity v p is determined.

In the equation, ΔI represents the distance between the ends of the particle clusters in consecutive frames, measured in meters; Δn is the number of frames between measurements; and f is the filming frequency, measured in frames per second (FPS).

Using the high-speed camera, the velocity of 150 μm SiO? particles is tested. By replacing aluminum foils of different thicknesses, the corresponding membrane rupture pressure ratios are obtained, which in turn allows for the determination of the impact velocity. The velocities corresponding to different aluminum foil thicknesses are summarized in Table 1. The specific calculation method for particle velocity can be found in the referenced literature.

Experimental Method

Before the experiment, the nickel-based carbide specimens are first polished using 1000# sandpaper. The specimens are then cleaned with an ultrasonic cleaner, air-dried, and weighed to obtain an average value. The specimens are fixed onto the specimen holder, and the angle of the specimen and the distance between the shock tube and the specimen are adjusted. The temperature control system is activated, and the experimental temperature is set. Aluminum foils of the appropriate thickness are selected and solid particles are loaded simultaneously.

The lighting is turned on, and the dynamic testing analyzer and high-speed camera are activated. The camera lens height is adjusted so that the distance from the shock tube outlet to the specimen surface is within the field of view of the high-speed camera. The nitrogen gas valve is then opened to start the experiment. When the aluminum foil ruptures, the valve is immediately closed, and the high-speed camera captures the particle trajectories during the experiment.

At the end of the experiment, the specimen is cooled, cleaned, and dried. The specimen is weighed 10 times using an electronic balance to record the average weight. The erosion-wear rate is then calculated using equation (2).

In the equation, E represents the erosion-wear rate, measured in mg/g; Δm is the mass loss of the material, measured in mg; and m p is the mass of a single impact particle, measured in grams.

Analysis and Discussion of Erosion-Wear Experimental Results

Effect of Impact Angle on YG8 Wear Rate

Under an impact velocity of 175 m/s, the erosion-wear rates of the specimens were measured by varying the impact angles, as shown in Figure 4.?

From Figure 4, it can be observed that the erosion-wear rate of the specimen initially increases and then decreases as the impact angle increases. The erosion-wear rate reaches its peak at an impact angle of 75°. The experimental results indicate that YG8 is a typical brittle material, with the maximum erosion-wear rate occurring at high impact angles. The erosion-wear characteristics of YG8 are consistent with the behavior of brittle materials, where the erosion-wear rate varies with the impact angle.

Impact Angle on Coating Erosion-Wear Performance

Particle velocity is a crucial factor affecting the wear rate of materials. Impact experiments were conducted on specimens at impact angles of 30°, 60°, and 90° under three different impact velocities: 148 m/s, 175 m/s, and 200 m/s. The relationship between erosion-wear rate and particle impact velocity is shown.

Figure 5 demonstrates that, at all three impact angles, the erosion-wear rate of the material increases with increasing impact velocity. There is a critical impact velocity at which erosion-wear begins, related to the abrasive properties and the material’s characteristics. Erosion-wear occurs only when the velocity exceeds this critical value. Extensive erosion tests indicate that the erosion-wear rate has the following relationship with particle velocity:

E=kv” （3）

where

v is the particle velocity in m/s;

k is a constant; and

n is the velocity index. A higher

n value indicates that the erosion-wear rate of the material is more influenced by the particle impact velocity.

Fitting the experimental data to equation (3) yields velocity indices of 2.34, 2.27, and 2.28 for impact angles of 30°, 60°, and 90°, respectively, for YG8 material.

Analysis of Erosion-Wear Mechanisms

Analysis of the erosion-wear morphology of specimens at an impact angle of 90° reveals that the erosion-wear is primarily driven by the impact forces of the solid particles directly striking the composite layer. Due to the high brittleness of both tungsten carbide particles and the composite layer matrix, high-velocity solid particle impacts more readily induce plastic deformation or crack formation, leading to the development of pits and cracks.

During the erosion process, the abrasive quartz sand continuously impacts the surface, creating numerous pits. The edges of these pits accumulate material that has been deformed and squeezed out, forming a lip-like flange. With continued particle impacts, this flange is progressively eroded and stripped away due to repeated compression. The wear mechanism can be summarized as erosion-induced compression leading to pit formation and material detachment.

As the reinforcement phase, WC particles have much higher hardness and stiffness compared to quartz sand, which helps them better withstand the abrasive impacts. During the erosion-wear process, the coating undergoes cutting and plowing effects from the sharp edges of the abrasive particles, resulting in plastic deformation, progressive fatigue, and delamination. The protruding WC particles bear the brunt of the abrasive impact. Table 2 shows the elemental chemical composition of the specimen surface before and after the erosion experiments.

Conclusion

As the impact angle increases, the erosion-wear rate of YG8 material first increases and then decreases, reaching a maximum at an impact angle of 75°. YG8 exhibits the erosion-wear characteristics typical of brittle materials.

At impact angles of 30°, 60°, and 90°, the erosion-wear rate of YG8 material increases with rising impact velocity. The corresponding velocity indices, obtained from fitting the erosion-wear rate versus velocity relationship, are 2.34, 2.27, and 2.28, respectively.

The primary erosion-wear mechanism for YG8 material involves the formation of pits and microcracks on the material surface due to high-angle impacts. These features are caused by the detachment of Co and WC particles from the matrix and the development of microcracks under high-velocity impacts.

Experimental Methods

Raw Materials

The experiment uses coarse and extra-coarse WC powders from well-known suppliers, with their main characteristics shown in Table 1. Additionally, 2.0 μm cobalt powder from the same supplier was also used.

Experimental Methods

For the preparation of WC-10%Co (where all content is given in weight percentage), weigh 900 g of WC, 100 g of Co, and 20 g of PEG. Measure 235 mL of alcohol and 2000 g of grinding balls. Add these into a 2.4 L ball mill. The mill is operated at a speed of 63 r/min for 14.5 hours. After milling, the mixture is dried, sieved, and then pressed into samples weighing 10 g each. The samples are sintered in a continuous vacuum sintering furnace at 1450°C.

Particle Size Measurement

For coarse tungsten carbide, measure the Fischer particle size in both the as-supplied and milled states. The samples are resin-mounted and analyzed using a metallurgical microscope to determine the grain size and particle size distribution of the powder. The alloy grain size and particle size distribution are measured using classic metallographic methods, and the coercive force of the samples is also assessed.

Results and Analysis

Fischer Particle Size (Fsss) and Alloy Grain Size

As-Supplied Particle Size and Alloy Grain Size

The metallographic images of alloys made from WC powders #1 and #2 are shown in Figures 1 and 2, respectively. Comparing Figures 1 and 2, it can be observed that the WC grain size in Figure 2 appears to be slightly coarser than in Figure 1. This indicates that coarser as-supplied Fsss particle sizes of WC lead to coarser grain sizes in the WC-Co alloys. Metallographic analysis shows that the average WC grain sizes for alloys made from powders #1 and #2 are 4.8 μm and 5.8 μm, respectively. Thus, the average grain size of WC in sample #2 is 1.2 times that in sample #1. The as-supplied Fsss particle size of #2 WC powder is 2.5 times that of #1 WC powder. Clearly, there is no direct proportional relationship between the as-supplied Fsss particle size of WC powder and the alloy grain size. Additionally, the Fsss particle size values for #1 WC powder are 2.5 times the alloy grain size, and for #2 WC powder, it is 5.3 times the alloy grain size. This indicates that the as-supplied WC powders for both samples are primarily aggregated polycrystalline WC particles, with more severe agglomeration for coarser WC powders.

Milled Particle Size and Alloy Grain Size

Comparing Table 1 with the metallographic grain sizes in Figures 1 and 2, it can be seen that the Fsss particle sizes of milled WC powders #1 and #2 are relatively close to the alloy grain sizes. Moreover, the measured alloy grain sizes are higher than the milled Fsss particle size values. This discrepancy is due to differences in measurement principles as well as grain growth during the sintering process. However, it clearly indicates that the Fsss particle sizes of coarse WC powders in the milled state are very close to the alloy grain sizes. The ratios of average grain sizes to milled particle sizes for alloys #1 and #2 are 1.15 and 1.31, respectively.

Raw Material WC Grain Size and Alloy Grain Size

Results from Direct Metallographic Measurement

Metallographic images of #1 and #2 WC powders after mounting and etching are shown in Figures 3 and 4. The grain sizes measured using metallographic methods are 5.31 μm and 8.5 μm, respectively. The grain size distributions of the powders and alloys are shown in Figures 5 and 6.

Figures 3 and 4 clearly indicate that the grain size of #2 WC is significantly larger than that of #1 WC. This suggests that WC with a coarser as-supplied Fischer particle size also has coarser grains. Additionally, it is evident that #1 WC exhibits better dispersion, with less pronounced sintering between particles compared to #2 WC. The severe sintering in #2 WC particles is a major reason why the metallographic grain size is much larger than the alloy grain size, and also explains why the grains in #2 WC are much larger than those in #1 WC.

From the grain size distribution of the raw powders and alloys in Figures 5 and 6, it can be seen that sample #1 contains coarse WC grains of 15–20 μm in the raw material, which are not present in the alloy. In contrast, sample #2 has a substantial amount of WC grains in the 15–35 μm range, though only a small amount of 15–20 μm grains are found in the alloy. This suggests that the severe sintering of the mounted WC, although difficult to distinguish by metallographic methods after etching, was fragmented during the intense grinding process.

Moreover, comparing the WC and alloy grain size distributions in Figures 5 and 6 shows that the grain size distribution of WC in sample #1 is more consistent with the alloy grain distribution than in sample #2. This consistency is a significant reason why many researchers believe that WC similar to sample #1 is more conducive to producing coarse alloys with a more uniform grain size.

WC Particle Size and Alloy Coercive Force

The coercive forces of the alloys made from #1 and #2 powders are 4.6 kA/m and 4.3 kA/m, respectively. The relationship between the WC-Co alloy grain size and the alloy’s coercive force can be expressed using the empirical formula (1).

In the formula:

• Hc= coercive force of the alloy (kA/m)
• Com= cobalt content in the alloy (%)
• Dwc= average WC grain size in the alloy (μm)

According to the calculations, the average grain sizes of alloys #1 and #2 are 7.4 μm and 8.8 μm, respectively. Clearly, the calculated grain sizes are significantly larger than the measured grain sizes, but the difference between the average grain sizes of alloys #2 and #1 is close to the difference observed using metallographic methods. The results obtained from formula (1) do not show a clear quantitative relationship with the Fsss particle sizes of the raw WC in both states, but the size of the raw material particles can still be used to predict the alloy grain size and coercive force.

Conclusions

Based on the above, the following conclusions can be drawn:

1.Coarse WC powders with larger as-supplied Fsss particle sizes tend to have higher milled Fsss particle sizes and larger grain sizes, leading to alloys with larger grain sizes.

2.The Fsss particle size in the milled state of coarse WC can be used to evaluate the grain size of coarse WC and predict the grain size of WC-Co alloys. Under the test conditions, the alloy grain size is 1.1 to 1.3 times the Fsss particle size of the milled WC.

3.Coarse WC powders with as-supplied Fsss particle sizes around 10 μm have a better consistency in grain size distribution with the alloy WC grain size distribution compared to extremely coarse WC powders with Fsss particle sizes above 25 μm.

Experimental Materials and Methods

Tungsten carbide (WC) powders were used as the raw material. Four different particle sizes of WC powder were selected: 4.0 μm, 2.2 μm, 1.1 μm, and 0.5 μm, which were labeled as WC1, WC2, WC3, and WC4, respectively. Metal cobalt (Co) powder was used as the binder phase, and paraffin was used as the forming agent. Four different WC-Co mixtures with varying particle sizes were prepared.

The mixtures were processed into green bodies with specific shapes and densities using extrusion forming equipment. The pressed green bodies were then placed in a sintering furnace and subjected to high-temperature sintering at 1400°C for 30 minutes, followed by cooling, to form cemented carbide bars.

The magnetic properties of the cemented carbide bars were tested using a magnetic performance tester, measuring parameters such as coercive force (Hc) and saturation magnetization (Bs), and the results were analyzed.

Experimental Results and Analysis

Effect of Particle Size on Coercive Force

As shown in Table 1, the coercive force of cemented carbide bars increases with decreasing WC particle size, while the saturation magnetization also increases. This indicates that cemented carbide bars made with fine and ultrafine WC particles exhibit poorer magnetic properties. Among the samples, the ultrafine WC (WC4) shows the highest coercive force of 4450 A/m, followed by medium-sized WC (WC3) with a coercive force of 3300 A/m. Coarse WC (WC2) and very coarse WC (WC1) have lower coercive forces, at 2350 A/m and 1200 A/m, respectively. The increase in coercive force with decreasing WC particle size is primarily due to the increase in internal defects and dislocations within smaller particles. These defects and dislocations create resistance to domain wall movement, making the magnetization process more difficult and requiring a larger external magnetic field to achieve saturation, thereby increasing the coercive force.

Effect of Particle Size on Material Magnetic Performance Stability

For fine and ultrafine WC particles, the larger grain boundary area facilitates grain boundary diffusion and reactions, which reduces the material’s magnetic properties. As the WC particle size decreases, the magnetic saturation of cemented carbide bars gradually increases. Specifically: coarse WC (WC1) exhibits the lowest magnetic saturation at only 1.25 T; medium-sized WC (WC2) has a magnetic saturation of 1.15 T; fine WC (WC3) and ultrafine WC (WC4) show higher magnetic saturations at 1.05 T and 0.93 T, respectively. This is likely because fine and ultrafine WC particles have higher chemical reactivity, promoting the diffusion and bonding of the Co binder, thereby improving the stability of the material’s magnetic performance.

Magnetic saturation is an indicator of the remaining proportion of magnetizable material and is closely related to magnetic properties such as coercive force and remanence. The impact of WC particle size on magnetic saturation can be attributed to the degree of solubility of the binder phase in the cemented carbide bars. Coarse and medium-sized WC particles, having larger specific surface areas, have more contact with the Co binder, which enhances the solubility of Co in the cemented carbide bars. This effectively improves the material’s magnetic performance stability, resulting in higher coercive force and better magnetic stability. Conversely, fine and ultrafine WC particles, with smaller specific surface areas, reduce the effectiveness of the Co binder, potentially affecting the material’s hardness and magnetic properties. Thus, selecting the appropriate particle size during the preparation of cemented carbide bars is crucial for achieving the best overall performance based on specific application needs.

Impact of Gamma Phase on Material Performance

For cemented carbide materials, the proportion of the gamma phase directly affects the material’s hardness and magnetic properties. Variations in carbon and oxygen content also influence the gamma phase proportion and must be considered during material preparation. Generally, higher carbon content leads to an increase in the gamma phase proportion, thereby enhancing the material’s hardness and magnetic performance. Therefore, different WC particle sizes may have varying carbon and oxygen contents, which also affects the gamma phase proportion and the overall performance of the material.

Discussion on Sintering Atmosphere

In the sintering process of cemented carbides, the choice and control of the atmosphere have a decisive impact on the final microstructure and magnetic properties of the material. The atmosphere not only affects the chemical reactions during sintering but also directly relates to the microstructure and final performance of the cemented carbide. The types of sintering atmospheres are as follows:

Oxidizing Atmosphere:? air.

Reducing Atmosphere: Contains components such as H? or CO: hydrogen atmosphere for cemented carbide sintering.

Inert or Neutral Atmosphere: Argon, helium, vacuum.

Carburizing Atmosphere: Contains high components that cause carburization of the sintered body, such as CO, methane, and hydrocarbon gases.

Nitrogen-Based Atmosphere: High nitrogen content sintering atmosphere: 10% H? in N?.

We mainly selected vacuum, argon, and hydrogen atmospheres for discussion. The variations in coercive force and magnetic saturation of cemented carbides sintered in argon, vacuum, and hydrogen atmospheres differ depending on the atmosphere, as shown in Table 2.

From Table 2, it can be observed that under vacuum and argon atmospheres, the coercive force (Hc) of cemented carbide bar is higher compared to that in a hydrogen atmosphere. Conversely, the saturation magnetization (Bs) is lowest in a hydrogen atmosphere compared to vacuum and argon atmospheres.

Under vacuum and argon atmospheres, the effective control of oxygen partial pressure and the exclusion of volatile elements result in fewer pores and inclusions, clearer grain boundaries, and better grain growth, thereby enhancing the magnetic properties of the material. In contrast, in a hydrogen atmosphere, the reducing nature of hydrogen may reduce some elements in the cemented carbide, leading to the presence of uncertain phase components, poor grain growth, and subsequently affecting the material’s magnetic properties.

For coercive force (Hc), it is largely dependent on the material’s microstructure and magnetic anisotropy. Under vacuum and argon atmospheres, effective control of oxygen partial pressure and exclusion of volatile elements reduce magnetic anisotropy in the cemented carbide, which improves coercive force. However, in a hydrogen atmosphere, hydrogen’s reducing effect can lead to the reduction of some elements in the cemented carbide, resulting in grain defects and inclusions that directly affect magnetic anisotropy and reduce coercive force.

Regarding saturation magnetization (Bs), the relative magnetic saturation value in cemented carbide is influenced by factors affecting carbon content in the alloy. In vacuum or argon atmospheres, effective control of oxygen content reduces carbon loss. Although the pressed green body contains oxygen, which can be reduced by free carbon and carbon in WC (MeO + C = Me + CO), the oxygen content in these atmospheres is relatively low. In a hydrogen atmosphere, decarburization reactions (WC + 2H? → CH? + C) begin at around 100°C. Throughout the preparation process, the material is exposed to a decarburizing atmosphere, leading to a lower relative magnetic saturation value.

Conclusion

This experiment investigated the effects of different particle sizes and sintering atmospheres on the magnetic properties of cemented carbide bars. By comparing the magnetic properties of cemented carbide under different WC particle sizes (coarse, medium, fine, and ultrafine) and sintering atmospheres (vacuum, argon, and hydrogen), it was found that both particle size and atmosphere have a significant impact on the magnetic performance of the material.

From the perspective of particle size, as the WC particle size decreases, the coercive force of the cemented carbide bars increases, while magnetic saturation also increases. This indicates that particle size has a substantial effect on the magnetic properties of cemented carbide. Fine and ultrafine WC particles, due to their higher chemical reactivity and good sintering performance, can promote the diffusion and bonding of the Co binder, thus enhancing the stability of the material’s magnetic performance. However, smaller particle sizes may lead to increased porosity and inclusions, affecting the material’s hardness and magnetic performance. Therefore, the choice of particle size should be tailored to the specific application needs when preparing cemented carbide.

Regarding the atmosphere, cemented carbide bars sintered under vacuum and argon atmospheres exhibited higher coercive force and better magnetic stability. This is because these atmospheres effectively control the oxygen content and volatile elements, reducing porosity and inclusions, and promoting clearer grain boundaries and grain growth. In contrast, cemented carbide bars sintered in a hydrogen atmosphere showed significantly lower magnetic saturation. This is likely due to the decarburizing effect of hydrogen. Therefore, selecting the appropriate sintering atmosphere is crucial for obtaining cemented carbide bars with excellent magnetic properties. Further improvements in cemented carbide performance can be achieved by optimizing sintering process parameters and adding suppressants.

The Effect of Cobalt Content

Figure 3 shows the microstructure after oxidation of carbides?with different cobalt contents (all WC materials are WC-1). As the cobalt content increases, the microstructure of the carbide?oxides changes significantly. The oxide of the WC-6%Co carbide?has more and larger pores, the pores in the oxide of the WC-10%Co carbide?are significantly reduced, and the oxide of the WC-14%Co carbide?has virtually no large pores.

Figure 4 shows the oxidation weight gain curves of carbides?with different cobalt contents. As the cobalt content increases, the oxidation weight gain of the carbides decreases sequentially. At 900°C, the oxidation weight gain of WC-6%Co, WC-10%Co, and WC-14%Co carbides are 11.92%, 11.46%, and 11.26%, respectively. Compared to WC-6%Co carbide, the oxidation weight gain of WC-10%Co and WC-14%Co carbides?at 900°C decreased by 3.8% and 5.5%, respectively. Therefore, although increasing the Co content can improve the high-temperature oxidation resistance of carbides, the improvement is not significant.

Table 3 lists the oxidation reaction equations of each component in the carbide?and their Gibbs free energy. It is well known that during the oxidation of carbides, the oxidation of WC to WO3 results in significant volume expansion. The oxide WO3 is loose, porous, and volatile, producing volatile gases such as CO2, which provide more pathways for the oxidation diffusion process, thereby exacerbating the oxidation of the carbide. Although the binder phase is more prone to oxidation than the hard phase, the oxide formed from the binder phase is the relatively dense CoWO4, which can slow down the oxidation diffusion process of the carbide. Therefore, with the increase in cobalt content, more CoWO4 and less WO3 are formed, resulting in a denser microstructure of the oxides and consequently improving the high-temperature oxidation resistance of the carbide.

Table 4 shows the room temperature hardness and high-temperature hardness of carbides?with different cobalt contents. At room temperature, the more cobalt content, the lower the hardness of the carbide. When the temperature rises to 800°C, the hardness of the carbides decreases significantly, with the rate of decrease reducing as the cobalt content increases. At 800°C, the hardness of carbides with higher cobalt content is actually higher than that of carbides with lower cobalt content.

Both the hard phase and the binder phase exhibit some thermal expansion at high temperatures, with the binder phase experiencing greater thermal expansion and generating larger stress, which offsets some of the load force. This is one of the reasons why the high-temperature hardness of the carbide?increases with the increase in cobalt content.

The Effect of WC Grain Size

Figure 6 shows the oxidation weight gain curves of 4#, 5#, and 6# carbides?prepared with WC of different Fischer particle sizes. From room temperature to 825°C, the oxidation weight gain curves of the three carbides with different WC grain sizes overlap; however, in the range of 825-900°C, the finer the WC grains, the less the oxidation weight gain of the carbides. At 900°C, the oxidation weight gains of 4#, 5#, and 6# carbides?are 9.18%, 8.67%, and 8.20%, respectively. Compared to the 4# carbide, the oxidation weight gain of the 5# and 6# carbides?at 900°C decreased by 5.6% and 10.7%, respectively. Therefore, under the same Co content, refining the WC grains can improve the high-temperature oxidation resistance of carbides.

Figure 7 shows the XRD diffraction patterns after oxidation of carbides?with different WC grain sizes. Since the compositions of 4#, 5#, and 6# carbides?are the same, there is no significant difference in their oxidation products. Therefore, the diffraction patterns of the oxides of the three carbides?with different WC grain sizes are essentially identical.

The Oxidation Resistance and hardness Differences of Carbides with Different WC Grain Sizes

The differences in the oxidation resistance of carbides?with different WC grain sizes can be mainly attributed to the following two points:

In the case of a uniform carbide?structure, finer WC grains result in more phase boundaries between WC and the binder phase. The finer WC grains are better encapsulated by the binder phase, and the oxidation products of the binder phase can, to some extent, hinder the oxidation diffusion process, thereby improving the high-temperature oxidation resistance of the carbide.

Finer WC grains have fewer grain boundary defects and smaller grain boundary voids between the WC grains, which correspondingly reduce the oxidation diffusion channels, thus enhancing the high-temperature oxidation performance of the carbide.

Table 5 shows the room temperature hardness and high-temperature hardness of carbides?with different WC grain sizes. At room temperature, the finer the WC grains, the higher the hardness of the carbide. When the temperature rises to 800°C, the hardness of the carbides decreases significantly, and the rate of decrease in high-temperature hardness increases as the WC grain size decreases. Clearly, although the room temperature hardness of the carbide?increases as the WC grain size decreases, the high-temperature hardness becomes lower.

The Effect of TaC/NbC/TiC Additives

Figure 8 shows the oxidation weight gain curves of carbides?with different carbide additives (all WC materials are WC-3). The oxidation weight gain curves and oxide diffraction patterns of WC-Co and WC-Co-TaC carbides?are basically the same, with oxidation weight gains of 10.58% and 10.20% at 900°C, respectively. Among the four carbides, WC-Co-NbC carbide?has the highest oxidation weight gain, while WC-Co-TiC carbide?has the lowest oxidation weight gain, with oxidation weight gains of 11.68% and 9.05% at 900°C, respectively.

Figure 9 shows the XRD diffraction patterns of carbides?with different carbide additives after oxidation. The oxidation of the carbides produces corresponding oxides.

In WC-Co carbides, the added TaC, NbC, and TiC all exist in the form of W-containing solid solutions. The (Nb,W)C solid solution oxidizes earlier than WC and has many phase boundaries with WC. Without the protective “encapsulation” of the binder phase, the oxidation of the solid solution promotes the oxidation of WC, thereby accelerating the oxidation of the carbide. The oxidation weight gain of WC-Co-TaC carbide?is the same as that of WC-Co carbide. This is because the (Ta,W)C solid solution reacts simultaneously with WC, and since the hard phase WC is the main component, the loose and porous WO3 phase predominantly controls the oxidation rate of the carbide. Therefore, the addition of TaC does not significantly affect the high-temperature oxidation resistance of the carbide.

In summary, under the same conditions of grain size and cobalt content, the addition of TaC has no significant effect on the high-temperature oxidation resistance of the carbide. However, the addition of NbC significantly reduces the high-temperature oxidation resistance of the carbide, with a reduction of 10.4%, while the addition of TiC significantly improves the high-temperature oxidation resistance of the carbide, with an improvement of 14.5%.

Table 6 shows the room temperature hardness and high-temperature hardness of carbides?with different carbide additives. At room temperature, the hardness of the carbides with TaC, NbC, and TiC additives is comparable to that of the WC-Co carbide. When the temperature rises to 800°C, the high-temperature hardness of the carbides with TaC, NbC, and TiC additives is higher than that of the WC-Co carbide, and the rate of decrease in high-temperature hardness is significantly reduced.

It is well known that solid solutions exhibit good red hardness and provide structural support to the overall carbide, helping it maintain high hardness under high-temperature conditions. Additionally, the solid solutions contribute to solid solution strengthening of the Co phase, which increases the hardness of the Co phase. Therefore, the addition of TaC, NbC, and TiC results in carbides?exhibiting good high-temperature hardness.

Conclusion

This study investigated the effects of cobalt content, WC grain size, and types of solid solutions on the high-temperature oxidation resistance and high-temperature hardness of carbides. The conclusions are as follows:

1.Increasing the cobalt content improves the high-temperature oxidation resistance of the carbide?and significantly increases the high-temperature hardness.

2.Reducing the WC grain size enhances the high-temperature oxidation resistance of the carbide?but significantly reduces the high-temperature hardness.

3.Compared to WC-Co carbides, the addition of TaC has no significant effect on the high-temperature oxidation resistance of the carbide, the addition of NbC decreases the high-temperature oxidation resistance, and the addition of TiC significantly improves the high-temperature oxidation resistance. All three additives, TaC, NbC, and TiC, significantly enhance the high-temperature hardness of the carbide.