Mechanisms of Grain Growth Inhibition

The grain growth inhibitors primarily influence WC grain growth through the following approaches:

Solute Drag Effect

Principle:grain growth Inhibitor elements (e.g., V, Cr) dissolve into the WC or Co phase, adsorb at WC/Co phase boundaries or WC/WC grain boundaries, hindering atomic diffusion and grain boundary migration.

Elemental Solid Solution

Inhibitors such as VC and Cr?C? decompose during sintering, with V and Cr atoms dissolving into the WC lattice or Co binder phase.

Example: V substitutes W sites in WC (forming (V,W)C solid solution), while Cr dissolves into the Co phase (forming (Co,Cr) solid solution).

Grain Boundary Segregation

Solute atoms (e.g., V, Cr) enrich at WC grain boundaries or WC/Co interfaces, forming a “solute atmosphere.”

These segregated atoms pin grain boundaries, increasing the energy barrier for migration.

Drag on Grain Boundary Movement

When grain boundaries attempt to migrate, solute atoms must move along, but their slower diffusion rate impedes boundary motion.

Analogous to “viscous drag,” this suppresses WC grain coalescence and growth.

Applicable grain growth Inhibitors: VC, Cr?C? (primarily rely on solute drag).

Second-Phase Pinning Effect (Zener Pinning)

Principle: grain growth inhibitors form nanoscale carbide particles (e.g., (V,W)C, (Cr,W)C) that physically obstruct WC grain growth at boundaries.

Nanoparticle Precipitation

During sintering, decomposed VC or Cr?C? reprecipitate as nanoscale carbides (e.g., 5–50 nm (V,W)C particles), typically located at WC/WC or WC/Co interfaces.

Grain Boundary Pinning

Migrating boundaries must overcome the restraint of these nanoparticles, requiring additional energy.

According to the Zener equation, pinning force (F?) correlates with particle volume fraction (f) and size (r). Finer, denser particles yield stronger inhibition.

Suppression of WC Dissolution-Reprecipitation

Nanoparticles hinder WC dissolution in liquid Co and redeposition, reducing Ostwald ripening (“large grains consuming small ones”).

Applicable grain growth Inhibitors: VC (strongest pinning), Cr?C? (moderate), TaC/NbC (weaker).

Common Grain Growth Inhibitors and Their Characteristics

Selection and Optimization of grain growth Inhibitors

Ranking of Inhibition Effectiveness

VC > Cr?C? > TaC ≈ NbC

Key Influencing Factors

Sintering Temperature and Time:

High temperatures or prolonged sintering may weaken inhibitor effectiveness (e.g., VC particle coarsening).

Co Content

Alloys with higher Co require greater grain growth inhibitor content (due to enhanced WC dissolution in liquid Co).

Carbon Balance

Inhibitors may consume free carbon, necessitating carbon potential adjustment to avoid η-phase formation (e.g., Co?W?C).

Detailed Industrial Application Cases of Cemented Carbide Grain Growth Inhibitors

Grain growth inhibitors (e.g., VC, Cr?C?, TaC) are widely used in the cemented carbide industry, primarily in cutting tools, mining tools, and wear-resistant components. The selection of different inhibitors directly affects the alloy’s hardness, toughness, wear resistance, and high-temperature stability. Below is an in-depth analysis of several typical application cases.

Ultra-Fine Grain Cemented Carbide Cutting Tools (VC + Cr?C? Composite Inhibition)

Application Background

Requirement: High-speed cutting and precision machining (e.g., automotive engine blocks, aerospace titanium alloys) demand tools with both high hardness (>90 HRA) and chipping resistance.

Issue

Conventional WC-Co alloys have coarse grains (1–3 μm), exhibiting high hardness but low toughness, leading to edge chipping.

Solution

Ultra-fine grain cemented carbide (grain size 0.2–0.5 μm) achieved through VC (0.3–0.5 wt%) + Cr?C? (0.5–1.0 wt%) composite addition.

Inhibition Mechanism

VC: Nano-sized (V,W)C particles pin WC grain boundaries (Zener pinning), suppressing grain coalescence.

Cr?C?: Cr dissolves into the Co phase, reducing WC dissolution rate (solute drag) while enhancing oxidation resistance.

Representative Products

Sandvik GC4325: For titanium alloy machining, using VC+Cr?C? inhibition (0.3 μm grains).

Kennametal KCS10B: For stainless steel finishing, incorporating nano-VC.

Mining Cemented Carbide Drill Bits (TaC/NbC High-Temperature Inhibition)

Application Background

Requirement: Oil drill bits and tunnel boring machine cutters operate under high temperatures (>800°C) and impact loads, requiring thermal fatigue resistance and wear resistance.

Issue

Conventional WC-Co alloys experience rapid grain growth at high temperatures, reducing strength.

Solution

TaC (1–3 wt%) or NbC (1–2 wt%) addition to leverage their high-temperature stability for grain growth suppression.

Inhibition Mechanism

TaC/NbC: Form (Ta,W)C or (Nb,W)C solid solutions at high temperatures, pinning grain boundaries (Zener effect) and reducing boundary mobility.

Synergy with Co binder: Ta/Nb dissolution into Co increases liquid Co viscosity, slowing WC dissolution-reprecipitation.

Representative Products

Atlas Copco Button Bits: TaC-containing drill bits for granite drilling.

Sumitomo Electric DX Series: Oil drilling alloys with NbC for thermal stability.

Wear-Resistant Sealing Rings (Cr?C? Inhibition + Rare Earth Optimization)

Application Background

Requirement: Mechanical seals and bearing sleeves require high wear resistance + corrosion resistance (e.g., chemical pumps, seawater environments).

Issue

WC-Co suffers from selective corrosion of the Co phase in corrosive media, causing WC grain detachment.

Solution

Cr?C? (1.0–1.5 wt%) + rare earth oxides (Y?O? 0.1–0.3 wt%) composite addition.

Inhibition Mechanism:

Cr?C?: Forms (Cr,W)C particles to refine grains while improving corrosion resistance via Cr dissolution in Co.

Y?O?: Rare earth elements segregate at grain boundaries, purifying interfaces and strengthening boundary cohesion.

Representative Products

Mitsubishi Materials EX Series: Chemical pump seals with Cr?C? + rare earth modification.

Oerlikon Durit CR: Corrosion-resistant alloys with Cr?C?.

PCB Micro-Drills (Ultra-Fine VC + Sintering Process Optimization)

Application Background

Requirement: PCB micro-drills (diameter 0.1–0.3 mm) demand ultra-high precision (roundness <1 μm) and fatigue resistance.

Issue

Grain coarsening causes drill edge blunting and fracture during drilling.

Solution

Ultra-fine VC (0.2–0.4 wt%) + low-temperature sintering (1350°C, vs. conventional 1450°C).

Inhibition Mechanism

Nano-VC: Prepared via high-energy ball milling (<50 nm particles) for enhanced pinning.

Low-temperature sintering: Reduces Ostwald ripening time, preserving inhibitor efficacy.

Representative Products

Toshiba Tungaloy DLC-Coated Micro-Drills: Nano-VC inhibition technology.

TaeguTec PCB Drill: Optimized for high-layer PCBs.

Conclusion

Grain growth inhibitors in cemented carbides control grain size through solute drag and second-phase pinning mechanisms. Their selection must be optimized based on material composition, sintering processes, and performance requirements. Future trends favor nano-composite inhibitors and multi-component synergistic regulation to further enhance comprehensive material properties.

At present, the regions in China that are most active in the recycling and regeneration of waste cemented carbide include Jinan City in Shandong Province, Qinghe County in Hebei Province, Mudanjiang City in Heilongjiang Province, and Zhuzhou City and Changsha City in Hunan Province.

Economic Benefits of Recycling Waste Carbide

Tungsten is the main component of cemented carbide, accounting for almost 50% of the total tungsten usage in its production, with China’s share being around 40%. Relevant data indicate that the demand for cemented carbide in various countries will rise significantly from the end of this century to the beginning of the next. It is estimated that by 2000, the demand could reach 40,000 tons, about 1.5 times the current production. However, tungsten is a rare element, with a crustal abundance of only 1×10?%, and the currently exploitable tungsten is only sufficient for 50 years.

Although China is a major producer of tungsten, both its reserves and recoverable quantities are showing a decreasing trend. Therefore, the rational utilization and recycling of tungsten resources should be placed on our agenda as an urgent issue to be seriously studied. Assuming that China’s recycling rate of waste alloy increases from 10% to 20%, it would mean an annual increase of several hundred tons of tungsten production. This would require the provision of several thousand tons of tungsten concentrate (containing 65% WO?) as raw material, equivalent to the tungsten content of 220,000 tons of raw ore (with a grade of 0.5% WO?). Thus, vigorously recycling cemented carbide is of great significance for the rational utilization and protection of existing tungsten resources.

Another major component of cemented carbide is cobalt. Due to the lack of cobalt resources in China, a large amount of cobalt needs to be imported annually to meet production needs. At the current level, recycling several hundred tons of cemented carbide in China each year could recover several tens of tons of cobalt, thereby saving a significant amount of foreign exchange for?our?country.

Processing Techniques of Recycling Waste Carbide

It is reported that there are currently about 30 different processing techniques used for the recycling of waste cemented carbide. Below is a brief introduction to several of the most commonly used and effective techniques in production.

Nitrate Fusion Method

This method involves melting waste cemented carbide together with nitrate at temperatures ranging from 900°C to 1200°C, resulting in the formation of soluble sodium tungstate. The reaction equation is as follows:

At this stage, the cooled melt is crushed and then leached with water to obtain a sodium tungstate solution and cobalt residue, which are then processed through normal procedures.

The advantages and disadvantages of this method are as follows: it has a large processing capacity and a wide range of applications, but it suffers from low recovery rates, high costs, poor working conditions, and significant pollution.

High-Temperature Oxidation Method

This method involves placing the cemented carbide in a temperature range of 700–950°C to oxidize it in air or oxygen. During this process, oxygen reacts with the alloy through the following chemical reaction:

The oxidized product is a brittle substance that, when treated with sodium hydroxide or a mixture of sodium hydroxide and sodium carbonate in a high-pressure leaching device, yields a sodium tungstate solution. The cobalt remaining in the residue is separated out according to conventional processes.

Phosphoric acid leaching method

Immerse the waste carbide?in a phosphoric acid solution and leach at a temperature of 50-60°C. Phosphoric acid reacts with cobalt in the carbide?to form cobalt phosphate, which enters the solution and separates from tungsten carbide. The advantages and disadvantages are: since phosphoric acid is a weak acid, the problem of equipment corrosion is easily solved, making it suitable for processing various waste carbides. However, the recovered tungsten carbide has a high oxygen content, and the subsequent process flow is long.

Zinc melting method

React waste carbides with zinc at a temperature close to 900°C. The cobalt in the alloy forms a zinc-cobalt low-melting-point alloy, causing the tungsten carbide in the waste alloy to lose the cobalt’s bonding effect and become loose. Then, vacuum distillation is used to evaporate and recover the metal zinc.

After the zinc melting process, the waste carbide?consists of layers of tungsten carbide and cobalt layers arranged in a multi-layered and interlocking pattern. It is a loose bulk material, which, after crushing, becomes a recycled carbide?mixture.

The advantages and disadvantages of the zinc melting method are: the process and equipment are relatively simple, the actual recovery rate is high, the production process causes less pollution, and the recovered mixture can be used directly for the production of tungsten products. However, this method consumes a lot of energy, with an electricity consumption of 4000-10000 degrees for processing 1 ton of waste carbide, and the recovered material contains a small amount of zinc, which has a certain impact on product quality.

Sodium sulfate fusion method

This method involves reacting waste carbides with sodium sulfate at a temperature of 900-1000°C to form a molten tungstic acid. After cooling, it is then leached with hot water to obtain a sodium tungstate solution and cobalt slag. The reaction equation is as follows: (The specific reaction equation is not provided in the original text, so it cannot be translated here.)

Its advantages and disadvantages are: wide adaptability and large production capacity. The drawback is that sulfur dioxide gas is emitted during the production process.

Electrolysis fusion method of recycling waste carbide

This method involves placing the waste carbide?in an electrolytic cell as the anode, nickel plate as the cathode, and dilute hydrochloric acid as the electrolyte. After electrolysis, the cobalt in the carbide?enters the solution in the form of COCl?. The washed and ground WC can be directly used to produce alloys. This method yields pure products, is highly efficient, has simple equipment, and is easy to operate. It is particularly suitable for processing with high cobalt content and has high value for promotion and application.

Cold embrittlement method

The cold embrittlement method involves crushing the waste carbide?coarsely, removing impurities, and then using a high-speed air stream to inject the coarsely crushed carbide?into a vacuum chamber equipped with a carbide?paddle, followed by further crushing to obtain a mixture.

This method has a wide range of processing and treatment, and the production process does not cause environmental pollution, but the equipment cost is relatively high.

According to reports, the zinc dissolution method is widely used for the recycling of waste carbides in China at the current stage. Overseas, the most economical method is considered to be a combination of the zinc dissolution method and the cold embrittlement method. In summary, there are many methods for recycling and processing waste carbides, each with its own pros and cons. When selecting a method in practice, a comprehensive analysis and comparison should be conducted based on the type of waste carbide, the size of the production scale, equipment capacity, technical level, and the source of raw and auxiliary materials, to choose an advanced, reasonable, and economically significant process for production practice.

Technical and Economic Preliminary Evaluation of Several Process Methods for Recycling Waste Carbides

As mentioned earlier, the zinc fusion method, electrolysis dissolution method, and mechanical crushing method have all become the main industrial methods for recycling and regenerating waste carbides. The recycled and regenerated powders can be used to produce carbides through conventional processes, which undoubtedly promotes the full utilization of non-ferrous metal resources such as tungsten and cobalt, saves energy, reduces manufacturing costs, promotes the development of small and medium-sized enterprises, and provides employment for the unemployed. Among them, the powder produced by the electrolysis dissolution method is particularly good in quality with low impurity content, low energy consumption, moderate processing costs, and good economic benefits (the selling price of WC powder is only 60% to 70% of the conventional product). It is one of the main methods being vigorously developed in many regions of our country.

Summary

It should be pointed out that the recycling and regeneration of waste carbides is a new venture and an emerging industrial sector in the field of carbides, which should be affirmed and supported. At the same time, great attention must be paid to product quality in the work of recycling and utilizing waste carbides, especially since most enterprises are still at a relatively low level of manual workshop production. Many enterprises often focus only on economic benefits while neglecting the control and testing of the recycling process and powder quality, which is incorrect. In the future, enterprises engaged in this kind of production should continuously improve and enhance the recycling process and product quality, strengthen the recognition of the importance of “product quality is the life of the enterprise,” and must not be careless. Otherwise, it will be difficult to maintain a firm foothold in the fierce market competition for a long time, let alone continue to develop and grow.

1.Development of Cryogenic Treatment Process

Cryogenic treatment usually adopts liquid nitrogen cooling, which can cool the workpiece to below – 190 ℃. The microstructure of the treated material changes at low temperature, and some properties are improved. Cryogenic treatment was first proposed by the former Soviet Union in 1939. It was not until the 1960s that the United States applied the cryogenic treatment technology to the industry and began to use it mainly in the aviation field. In the 1970s, it expanded to the machinery manufacturing field.

According to different cooling methods, it can be divided into liquid method and gas method. The liquid method means that the material or workpiece is directly immersed in liquid nitrogen to cool the workpiece to liquid nitrogen temperature, and the workpiece is kept at this temperature for a certain period of time, then it is taken out and heated to a certain temperature. It is difficult to control the speed of temperature rise and fall in this way, which has a large thermal impact on the workpiece and is generally believed to be likely to cause damage to the workpiece. Cryogenic equipment is relatively simple, such as liquid nitrogen tank.

2.gas method?of Cryogenic treatment

The gas principle is to cool by the gasification latent heat of liquid nitrogen (about 199.54kJ/kg) and the heat absorption of low-temperature nitrogen. The gas method can make the cryogenic temperature reach – 190 ℃, so that the cryogenic nitrogen can contact the materials. Through convection heat exchange, the nitrogen can be vaporized in the cryogenic box after being ejected from the nozzle. The workpiece can be cooled by the latent heat of gasification and the heat absorption of cryogenic nitrogen. By controlling the input of liquid nitrogen to control the cooling rate, the cryogenic treatment temperature can be automatically adjusted and accurately controlled, and the thermal shock effect is small, so is the possibility of cracking.

At present, the gas method is widely recognized by researchers in its application, and its cooling equipment is mainly a programmable cryogenic box with controllable temperature. Cryogenic treatment can significantly improve the service life, wear resistance and dimensional stability of ferrous metals, nonferrous metals, metal alloys and other materials, with considerable economic benefits and market prospects.

The cryogenic technology of cemented carbide was first reported in the 1980s and 1990s. Mechanical Technology of Japan in 1981 and Modern Machine Shop of the United States in 1992 reported that the performance of cemented carbides was significantly improved after cryogenic treatment. Since the 1970s, the research work on cryogenic treatment abroad has been fruitful. The former Soviet Union, the United States, Japan and other countries have successfully used cryogenic treatment to improve the service life of tools and dies, wear resistance of workpieces and dimensional stability.

3.Strengthening mechanism of cryogenic treatment

Metal phase reinforcement.

Co in cemented carbides has fcc crystal structure α Phase (fcc) and close packed hexagonal crystal structure ε Phase (hcp). ε- Co ratio α- Co has small friction coefficient and strong wear resistance. Above 417 ℃ α The free energy of phase is low, so Co α Phase form exists. Below 417 ℃ ε Low free energy of phase, stable phase at high temperature α Phase transition to low free energy ε Phase. However, due to WC particles and α The existence of solid solution heteroatoms in the phase has a greater constraint on the phase transition, making α → ε When the phase change resistance increases and the temperature drops below 417 ℃ α The phase cannot be completely transformed into ε Phase. Cryogenic treatment can be greatly increased α And ε Two phase free energy difference, thus increasing the driving force of phase change ε Phase change variable. For the cemented carbide after cryogenic treatment, some atoms dissolved in Co precipitate in the form of compound due to the decrease of solubility, which can increase the hard phase in the Co matrix, hinder dislocation movement, and play a role in strengthening the second phase particles.

Strengthening of surface residual stress.

The study after cryogenic treatment shows that the surface residual compressive stress increases. Many researchers believe that a certain value of residual compressive stress in the surface layer can greatly improve its service life. During the cooling process of cemented carbide after sintering, the bonding phase Co is subject to tensile stress, and the WC particles are subject to compressive stress. The tensile stress has great damage to Co. Therefore, some researchers believe that the increase of surface compressive stress caused by deep cooling slows down or partially offsets the tensile stress generated by the bonding phase during the cooling process after sintering, or even adjusts it to compressive stress, reducing the generation of microcracks.

Other strengthening mechanisms

It is believed that η The phase particles together with WC particles make the matrix more compact and firm, and due to η The formation of the phase consumes the Co in the matrix. The decrease of Co content in the bonding phase increases the overall thermal conductivity of the material, and the increase of carbide particle size and adjacency also increases the thermal conductivity of the matrix. Due to the increase of thermal conductivity, the heat dissipation of tool and die tips is faster; The wear resistance and high temperature hardness of tools and dies are improved. Others believe that after cryogenic treatment, due to the shrinkage and densification of Co, the firm role of Co in holding WC particles is strengthened. Physicists believe that deep cooling has changed the structure of atoms and molecules of metals.

4.A Case of YG20 Cold Heading Die with Cryogenic Treatment

Operation steps of YG20 cold pier formwork cryogenic treatment:

(1) Put the sintered cold heading die into the cryogenic treatment furnace;

(2) Start the cryogenic tempering integrated furnace, open the liquid nitrogen, reduce it to – 60 ℃ at a certain rate, and keep the temperature for 1h;

(3) Reduce to – 120 ℃ at a certain rate, and keep the temperature for 2h;

(4) Reduce the temperature to – 190 ℃ at a certain cooling rate, and keep the temperature for 4-8h;

(5) After the heat preservation, the temperature shall be raised to 180 ℃ according to 0.5 ℃/min for 4h

(6) After the program equipment is completed, it will be automatically powered off and naturally cooled to room temperature.

Conclusion: The YG20 cold heading die without cryogenic treatment and after cryogenic treatment is cold headed Φ 3.8 Carbon steel screw rod, the results show that the service life of the die after cryogenic treatment is more than 15% longer than that of the die without cryogenic treatment.

It can be seen that compared with that before cryogenic treatment, the face centered cubic cobalt (fcc) in YG20 after cryogenic treatment is significantly reduced, ε- The obvious increase of Co (hcp) is also the reason for the improvement of wear resistance and comprehensive properties of cemented carbides.

5.Limitations of cryogenic treatment process

The practical application results of a tool and die company in the United States show that the service life of cemented carbide inserts after treatment is increased by 2~8 times, while the dressing cycle of cemented carbide wire drawing dies after treatment is extended from several weeks to several months. In the 1990s, domestic research on cryogenic technology of cemented carbide was carried out, and certain research results were achieved.

In general, the research on cryogenic treatment technology of cemented carbide is less developed and not systematic at present, and the conclusions obtained are also inconsistent, which needs further in-depth exploration by researchers. According to the existing research data, cryogenic treatment mainly improves the wear resistance and service life of cemented carbide, but has no obvious effect on physical properties.

Edge radius processing is an indispensable process after fine grinding of CNC tools and before coating. The purpose is to make the cutting edge smooth and smooth, and extend the tool life. There are 9 methods of edge radius treatment of CNC tools introduced by Meetyou. Let’s get to know it.

Edge radius?treatment of the cutting tools of the machining center refers to the process of leveling, polishing and deburring the cutting tools, including edge passivation, chip removal groove polishing and coating polishing.

1. Resistance to tool physical wear

In the cutting process, the tool surface will be gradually consumed by the workpiece, and the cutting edge is prone to plastic deformation under high temperature and high pressure. The passivation treatment of tools can help improve the rigidity of tools and avoid premature loss of cutting performance of tools.

2. Maintain the smoothness of the workpiece

Burrs on the cutting edge of the tool will cause tool wear, and the surface of the machined workpiece will become rough. After passivation treatment, the cutting edge of the tool will become very smooth, the phenomenon of edge collapse will be reduced accordingly, and the surface finish of the workpiece will also be improved.

3. Convenient groove chip removal

Polishing the tool groove can improve the surface quality and chip removal performance. The smoother the groove surface, the better chip removal will be, and more consistent cutting can be achieved.

After passivation and polishing, the tools of CNC machine tools will leave many small holes on the surface. These holes can absorb more cutting fluid during machining, which will greatly reduce the heat generated during cutting and greatly improve the cutting speed.

9 kinds of edge radius processing methods

Grinding wheel edge radius?method

This is the earliest and most widely used passivation technology.

Nylon brush?edge radius?method

it is a common method to coat the abrasive medium of fine particles on the brush wheel or brush disc of nylon material, and re move the cutter through the high-speed rotation of the brush.

Sand blasting method

it is divided into dry sand blasting and wet sand blasting. It is also a common method of edge radius processing. Compared with nylon brush method, this process accomplish?a higher consistency of edges.

Stirring method of edge radius processing

This method is to put the whole tool into the abrasive bucket before treatment, and position the depth of the tool through the laser sensor to ensure the quality of treatment. The blade consistency of this process is also higher than that of nylon brush method.

Electrochemical mechanical edge radius processing

This is a composite process that combines electrochemical machining and mechanical grinding. First, electrolytic deburring, and then mechanical grinding to remove oxide film.

Laser method: it is a passivation technology developed on the basis of laser cladding technology. It can produce high heat on the blade surface by laser, melt some materials, and achieve the effect of passivating the blade.

Vibration edge radius processing method

 the main processing device includes a vibration table and a worktable. The blade is placed in a container that is connected with the vibration body. The container is filled with abrasive particles. The abrasive particles and the blade repeatedly collide to remove trace materials on the cutting edge through collision to achieve edge passivation.

Magnetic abrasive method

This is a edge radius processing that applies a magnetic field in the direction perpendicular to the axis of the cylindrical surface of the workpiece, and adds magnetic abrasive between the magnetic field S and N poles. The magnetic abrasive will be adsorbed on the magnetic pole and the workpiece surface, and will be arranged into a flexible “abrasive brush” along the direction of the magnetic line of force. The cutter rotates and vibrates axially at the same time to remove the metal and burrs on the workpiece surface.

Micro abrasive water jet technology: a new and environment-friendly processing technology, which forms a liquid-solid high-energy jet through the control of the pressurizer and nozzle diameter, and realizes passivation treatment by high-speed and repeated collision on the workpiece.

Etching is a technology that uses chemical strong acid corrosion, mechanical polishing or electrochemical electrolysis to treat the surface of objects. In addition to enhancing aesthetics, it also increases the added value of objects. From traditional metal processing to high-tech semiconductor manufacturing, they are all within the scope of application of etching technology.

Metal etching is a technology to remove metal materials through chemical reaction or physical impact. Metal etching technology can be divided into wet etching and dry etching. Metal etching consists of a series of chemical processes. Different etchants have different corrosion characteristics and strength for different metal materials.

Metal etching, also known as photochemical etching, refers to the removal of the protective film of the metal etching area after exposure, plate making, development and contact with the chemical solution in the process of metal etching, so as to achieve dissolution corrosion, formation of bumps, or hollowing out. It was first used to manufacture printed concave convex plates such as copper plate and zinc plate. It is widely used to reduce the weight of instrument panel or process thin workpieces such as nameplate. Through the continuous improvement of technology and process equipment, etching technology has been applied to aviation, machinery, chemical industry and semiconductor manufacturing processes for the processing of precision metal etching products of electronic thin parts.

Types of etching technology

Wet etching:

Wet etching is to immerse the wafer into a suitable chemical solution or spray the chemical solution onto the wafer for quenching, and remove the atoms on the surface of the film through the chemical reaction between the solution and the etched object, so as to achieve the purpose of etching During wet etching, the reactants in the solution first diffuse through the stagnant boundary layer, and then reach the wafer surface to produce various products through chemical reactions. The products of etching chemical reaction are liquid or gas phase products, which are then diffused through the boundary layer and dissolved in the main solution. Wet etching will not only etch in the vertical direction, but also have the effect of horizontal etching.

Dry etching:

Dry etching is usually one of plasma etching or chemical etching. Due to different etching effects, the physical atoms of ions in the plasma, the chemical reaction of active free radicals and the surface atoms of devices (wafers), or the combination of the two, include the following contents:

physical etching: sputtering etching, ion beam etching

chemical etching: plasma etching

physicochemical composite etching: reactive ion etching (RIE)

Dry etching is a kind of anisotropic etching, which has good directivity, but the selectivity is worse than wet etching. In plasma etching, plasma is a partially dissociated gas, and gas molecules are dissociated into electrons, ions and other substances with high chemical activity. The biggest advantage of dry etching is “anisotropic etching”. However, the selectivity of dry etching is lower than that of wet etching. This is because the etching mechanism of dry etching is physical interaction; Therefore, the impact of ions can remove not only the etching film, but also the photoresist mask.

Etching process

According to the type of metal, the etching process will be different, but the general etching process is as follows: metal etching plate → cleaning and degreasing → water washing → drying → film coating or silk screen printing ink → drying → exposure drawing → development → water washing and drying → etching → film stripping → drying → inspection → finished product packaging.

1. Cleaning process before metal etching:

The process before etching stainless steel or other metals is cleaning treatment, which is mainly used to remove dirt, dust, oil stains, etc. on the material surface. The cleaning process is the key to ensure that the subsequent film or screen printing ink has good adhesion to the metal surface. Therefore, the oil stain and oxide film on the metal etching surface must be completely removed. Degreasing shall be determined according to the oil stain of the workpiece. It is best to degrease the silk screen printing ink before electric degreasing to ensure the degreasing effect. In addition to the oxide film, the best etching solution shall be selected according to the type of metal and film thickness to ensure surface cleanliness. It must be dry before screen printing. If there is moisture.

2. Paste dry film or silk screen photosensitive adhesive layer:

According to the actual product material, thickness and the exact width of the figure, it is determined to use dry film or wet film silk screen printing. For products with different thicknesses, factors such as the etching processing time required for product graphics should be considered when applying the photosensitive layer. It can make a thicker or thinner photosensitive adhesive layer with good coverage performance and high definition of patterns produced by metal etching.

3. Drying:

After the completion of film or roll screen printing ink, the photosensitive adhesive layer needs to be thoroughly dried to prepare for the exposure process. At the same time, ensure that the surface is clean and free of adhesion, impurities, etc.

4. Exposure:

This process is an important process of metal etching, and the exposure energy will be considered according to the thickness and accuracy of the product material. This is also the embodiment of the technical ability of etching enterprises. The exposure process determines whether the etching can ensure better dimensional control accuracy and other requirements.

5. Development:

After the photosensitive adhesive layer on the surface of the metal etching plate is exposed, the pattern adhesive layer is cured after exposure. Then, the unwanted part of the pattern, that is, the part that needs corrosion, is exposed. The development process also determines whether the final size of the product can meet the requirements. This process will completely remove the unnecessary photosensitive adhesive layer on the product.

6. Etching or etching process:

After the product prefabrication process is completed, the chemical solution will be etched. This process determines whether the final product is qualified. This process involves etching solution concentration, temperature, pressure, speed and other parameters. The quality of the product needs to be determined by these parameters.

7. Removal:

The surface of the etched product is still covered with a layer of photosensitive adhesive, and the photosensitive adhesive layer on the surface of the etched product needs to be removed. Because the photosensitive adhesive layer is acidic, it is mostly expanded by acid-base neutralization method. After overflow cleaning and ultrasonic cleaning, remove the photosensitive adhesive layer on the surface to prevent photosensitive adhesive residue.

8. Test:

After the film is taken, the following is testing, packaging, and the final product is confirmed whether it meets its specifications.

Precautions in etching process

reduce side corrosion and protruding edges and improve metal etching processing coefficient: generally, the longer the printed board is in the metal etching solution, the more serious the side etching is. Undercutting seriously affects the accuracy of printed wire, and serious undercutting will not make thin wire. When the undercut and edge decrease, the etching coefficient increases. The high etching coefficient indicates that the thin line can be maintained and the etched line is close to the size of the original image. Whether the plating resist is tin lead alloy, tin, tin nickel alloy or nickel, the excessively protruding edge will lead to short circuit of the conductor. Because the protruding edge is easy to break, an electric bridge is formed between two points of the conductor.

improve the consistency of etching processing rate between plates: in continuous plate etching, the more consistent the metal etching processing rate, the more uniform etching plate can be obtained. In order to maintain the best etching state in the pre etching process, it is necessary to select an etching solution that is easy to regenerate and compensate and easy to control the etching rate. Select technologies and equipment that can provide constant operating conditions and automatically control various solution parameters. It can be realized by controlling the amount of copper dissolved, pH value, solution concentration, temperature, uniformity of solution flow, etc.

improve the uniformity of the metal etching processing speed of the whole plate surface: the etching uniformity of the upper and lower sides of the plate and each part of the plate surface is determined by the uniformity of the flow rate of the metal etching solution on the plate surface. In the etching process, the etching rates of the upper and lower plates are often inconsistent. The etching rate of the lower plate surface is higher than that of the upper plate surface. Due to the accumulation of solution on the surface of the upper plate, the etching reaction is weakened. The uneven etching of the upper and lower plates can be solved by adjusting the injection pressure of the upper and lower nozzles. The spray system and the oscillating nozzles can further improve the uniformity of the whole surface by making the spray pressure of the center and edge of the plate different.

Advantages of etching process

Because the metal etching process is etched by chemical solution.

maintain high consistency with raw materials. It does not change the properties, stress, hardness, tensile strength, yield strength and ductility of the material. The base processing process is etched in the equipment in an atomized state, and there is no obvious pressure on the surface.

no burrs. In the process of product processing, there is no pressing force in the whole process, and there will be no crimping, bumping and pressing points.

it can cooperate with the post process stamping to complete the personalized molding action of the product. The hanging point method can be used for full plate electroplating, bonding, electrophoresis, blackening, etc., which is more cost-effective.

it can also cope with miniaturization and diversification, short cycle and low cost.

Application field of etching processing

consumer electronics

filtration and separation technology

Aerospace

medical equipment

precision machinery

car

high end crafts

Cemented carbide is a kind of cemented carbide which is made by powder metallurgy process from the hard compound of refractory metal and bonding metal. Because of its good hardness and strength, it is widely used in many fields. With the requirement of high temperature performance and corrosion resistance of cemented carbide materials getting higher and higher, the performance of existing cemented carbide materials is difficult to meet its use requirements. In the past 30 years, many scholars have carried out experimental research on WC based compounds and obtained a series of research results.

WC metals

WC-Co

The cementitious material widely used in tungsten carbide is cobalt. WC Co system has been studied extensively. The addition of CO makes WC have good wettability and adhesion. In addition, as shown in Figure 13.2, the addition of CO can also significantly improve the strength and toughness.

Figure 13.3 backscatter electron micrograph of WC Co powder showing the external and cross-sectional structures: (a), (b) F8; (c), (d) M8; and (E), (f) C8.

He performed backscatter electron imaging of F8, M8 and C8 powders and their polished sections. It was observed that all powders have typical spherical shape. F8 powder shows a dense accumulation of fine carbides, while M8 and C8 powder show a relatively loose accumulation structure with some pores. On the polished section, all samples show obvious scattering phenomenon, and the hardness and wear resistance are inversely proportional to the cobalt content. The Vickers hardness (HV) varies from 1500 to 2000 HV30, and the fracture toughness ranges from 7 to 15 MPa M1 / 2. This significant change is a function of carbide composition, microstructure and chemical purity.

Generally speaking, the smaller the particle size, the higher the hardness and the better the wear resistance. The higher the volume fraction of CO, the higher the fracture toughness, but the lower the hardness and wear resistance (Jia et al., 2007). Therefore, in order to obtain better performance, it is inevitable to consider using other cementitious materials instead.

On the other hand, because of the above reasons, it is not scientific in strategy and easy to affect the price trend. In addition, the combination of WC and co dust is worrisome because they are more lethal than any single use.

WC-Ni

Nickel is cheaper and easier to obtain than cobalt. It has a good toughening property. It can be used to improve corrosion / oxidation performance, high temperature strength and wear resistance in harsh environment. Compared with WC Co alloy, the plasticity of the material is lower. Because nickel dissolves well in WC, it is used as an adhesive for WC substrates, which results in a strong bond between them.

WC-Ag

The addition of Ag makes WC a kind of arc resistant material. Under the action of overload current, WC is often loaded in switching devices, which can be attributed to the well-known electrical contact resistance (RC) of the latter. It is worth mentioning that the resistivity of WC Ag composite decreases with the increase of Ag content, and the hardness decreases with the increase of Ag content, which is due to the great difference between the hardness of WC and Ag. In addition, the coarse WC grains have very low and stable contact resistance.

Figure 13.4 shows the average electrical contact resistance (RC) produced by the switch

Cycle 11e50 with different silver content and WC particle size, because RC of most materials is observed to be stable after 10 switching cycles. The contact resistance of silver is between 50-55 wt% (volume ratio 60% and 64.6%) in WC with a particle size of 4 mm, and between 55-60 wt% (volume ratio 64.6% and 69%) in WC with a particle size of 0.8 and 1.5 mm. Therefore, this determines the initial composition of the investment, where the Ag matrix is fully interconnected. For fixed components, a decrease in contact resistance between 1.5 and 4 mm WC particle size was observed, which also marks the permeation threshold.

WC-Re

Scientists are using tungsten carbide to strengthen rhenium in order to obtain better performance than WC Co, because RE can bring high temperature hardness and good combination

Figure 13.4 the ratio of the average electrical contact resistance at different Ag content and WC particle size to the contact resistance of the WC substrate during cycles 11 to 50 is co or Ni. According to the microstructure characteristics of WC coere (20% RE content), it is described that WC coere retained in CO and continued to form HCP structure, thus improving the hardness of the alloy. The researchers also strengthened re in WC Ni and found similar inferences. Due to its highest hardness and twice the durability of WC Co, the alloy is used to manufacture competitive tool parts. When cold pressing WC and Re powders followed by a patented hot pressing process, more than 2400 kg/mm~2 of HV was observed (compared to 1700 kg/mm~2 for WC-Co)

WC intermetallics

WC-FeAl

In the past few decades, intermetallic compounds as ceramic adhesives have attracted people’s attention. Iron aluminide has excellent oxidation resistance and corrosion resistance, low toxicity, high hardness, good wear resistance, high temperature stability and good wettability. It is thermodynamically suitable for WC as binder. The hardness and fracture toughness of WC FeAl and WC Co are basically the same. The hardness and wear resistance of WC Co alloy are similar to those of conventional WC Co alloy. It can be considered that if the grain size can be optimized, it is possible to replace the traditional WC Co. The particle size distribution curve of WC FeAl mixed powder prepared by different ball milling and / or drying processes is shown in Figure 13.5. The three curves in Figure 13.5 have bimodal distribution. In Figure 13.5, the left peak of the smaller particle size corresponds to the left peak of a single WC particle. The correct peak value of larger particle size corresponds to the peak value of FeAl fragments containing some WC particles. When the correct peak moves, the left peak does not depend on the grinding and / or drying process. The correct peak of D-R powder (dehydrated ethanol as solvent for rapid drying) shifts to the corresponding peak of the other two powders.

Figure 13.5 Particle size distributions of WC-FeAl mixed powders prepared from various powder processes.

WC-ceramics

WC-MgO

Wc-mgo composite materials have been widely used because of the addition of MgO particles in the WC matrix, which has little effect on the hardness and significantly improves the toughness of the materials. The hardness is inversely proportional to the toughness, but in the case of this alloy, the toughness is obtained when the hardness loss is very small. Adding a small amount of VC, Cr3C2 and other grain growth inhibitors to the studied material can not only control the grain growth in the sintering process, but also improve the mechanical properties of the material.

WC-Al2O3

It must be mentioned here that Al2O3 is used as a reinforcing material for WC, and vice versa, because of their excellent mechanical and physical properties.

Sintering temperature and holding time have significant effects on the microstructure and mechanical properties of wc-40vol% Al2O3 composite. With the increase of sintering temperature and holding time, the relative density and particle size increase. At the same time, the values of high pressure and fracture toughness increase first and then decrease. The microstructure of crack path reveals the existence of crack bridging and crack deflection. In wc-40vol% Al 2O 3 composites, the main toughening mechanism is the generation of secondary and lateral cracks. Another study shows that HV is about 20e25gpa and fracture toughness is 5e6mpa.m1/2.

Figure 13.6 shows the variation trend of hardness, fracture toughness and transverse fracture strength with alumina content. It should be noted that these values are quite different from those reported (Mao et al., 2015). Pure WC has the highest hardness and the lowest fracture toughness. The addition of Al2O3 improves the fracture toughness, but the hardness of pure alumina is lower than that of pure WC, and the hardness of wc-al2o3 composite decreases. The different results in Figure 13.6 show that the mechanical properties depend not only on the alumina content, but also on the production process and grade of different substrates. 

WC abrasives

WC cBN

Because CBN has excellent hardness, thermal stability and reaction activity with iron, adding CBN to WC Co can improve the wear resistance, hardness and mechanical properties of the material. Once CBN is strengthened into WC matrix, strong adhesion will be produced. In addition, better fracture toughness can be obtained by crack deflection or bridging of CBN particles. The two main obstacles in the process of CBN addition are the conversion from CBN to hBN and the strong covalent bonding between B and N, which results in the low sintering ability of CBN and cemented carbide.

WC diamonds

WC diamond has excellent fracture toughness, crack growth resistance and reflection resistance. This material can only be produced under thermodynamic conditions to prevent diamond from turning into graphite. Through more research to improve the performance of this material, we can make up the huge cost gap, which is very necessary.

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introductionSteel is quenched by heating the steel to a temperature above the critical temperature Ac3 (hypo-eutectoid steel) or Ac1 (hypereutectoid steel), holding it for a period of time so as to be austenitized in whole or in part, and then cooled at a temperature greater than the critical cooling rate Rapid cooling to below the Ms (or Ms near the isothermal) martensitic (or bainite) heat treatment process. The solution treatment of materials such as aluminum alloys, copper alloys, titanium alloys, toughened glass, etc., or heat treatment processes with rapid cooling is also commonly referred to as quenching. Quenching is a common heat treatment process, mainly used to increase the hardness of the material. Usually from the quenching medium, can be divided into water quenching, oil quenching, organic quenching. With the development of science and technology, some new quenching processes have emerged.1 high-pressure air-cooled quenching methodWorkpieces in the strong inert gas flow quickly and evenly cooling, to prevent surface oxidation, to avoid cracking, reduce distortion, to ensure that the required hardness, mainly for tool steel quenching. This technology has recently progressed rapidly and the range of applications has also expanded considerably. At present, the vacuum gas quenching technology developed rapidly, and the negative pressure (<1 × 105 Pa) high flow rate gas cooling followed by gas cooling and high pressure (1 × 105 ~ 4 × 105 Pa) 10 × 105 Pa) air-cooled, ultra-high pressure (10 × 105 ~ 20 × 105 Pa) air-cooled and other new technologies not only greatly enhance the vacuum quenching ability of air-cooled, and quenched the workpiece surface brightness is good, small deformation, but also A high efficiency, energy saving, pollution-free and so on. The use of vacuum high-pressure gas-cooled quenching is the quenching and tempering of materials, the solution, aging, ion carburizing and carbonitriding of stainless steel and special alloys, as well as vacuum sintering, cooling and quenching after brazing. With 6 × 105 Pa high pressure nitrogen cooling quenching, the load can only be cooled loose, high-speed steel (W6Mo5Cr4V2) can be hardened to 70 ~ 100 mm, high alloy hot work die steel up to 25 ~ 100 mm, gold Cold work die steel (such as Cr12) up to 80 ~ 100 mm. When quenched with 10 × 10 5 Pa of high pressure nitrogen, the cooled load can be intensive, increasing the load density by about 30% to 40% over cooling of 6 × 10 5 Pa. When quenched with 20 × 10 5 Pa of ultra-high pressure nitrogen or a mixture of helium and nitrogen, the cooled loads are dense and can be bundled together. The density of 6 × 105 Pa nitrogen cooling 80% to 150%, can be cooled all high-speed steel, high alloy steel, hot work tool steel and Cr13% chromium steel and more alloy oil quenched steel, such as more Large-size 9Mn2V steel. Dual-chamber air-cooled quench furnaces with separate cooling chambers have better cooling capacity than the same type of single chamber furnaces. The 2 × 105 Pa nitrogen cooled double chamber furnace has the same cooling effect as the 4 × 105 Pa single chamber furnace. However, operating costs, low maintenance costs. As China’s basic materials industry (graphite, molybdenum, etc.) and ancillary components (motor) and other levels to be improved. Therefore, to improve the 6 × 105 Pa single-chamber high-pressure vacuum care while maintaining the development of dual-chamber pressure and high-pressure air-cooled quenching furnace more in line with China’s national conditions.Figure 1 high-pressure air-cooled vacuum furnace2 strong quenching methodConventional quenching is usually with oil, water or polymer solution cooling, and strong quenching rule with water or low concentrations of salt water. Strong quenching is characterized by extremely fast cooling, without having to worry about excessive distortion of steel and cracking. Conventional quench cooling to the quenching temperature, the steel surface tension or low stress state, and strong quenching in the middle of cooling, the workpiece heart is still in the hot state to stop cooling, so that the formation of surface compressive stress. Under the severe quenching condition, the supercooled austenite on the surface of the steel is subjected to compressive stress of 1200 MPa when the cooling rate of the martensitic transformation zone is higher than 30 ℃ / s, so that the yield strength of the steel after quenching is increased by at least 25%.Principle: Steel from austenitizing temperature quenching, the temperature difference between the surface and the heart will lead to internal stress. Phase change of the specific volume of phase change and phase change plastic will also cause additional phase transformation stress. If the thermal stress and phase transition stress superposition, that is, the overall stress exceeds the yield strength of the material will be plastic deformation occurs; if the stress exceeds the tensile strength of hot steel will form a quenching crack. During intensive quenching, the residual stress caused by the phase change plasticity and the residual stress increase due to the specific volume change of austenite-martensite transformation. In the intense cooling, the workpiece surface immediately cooled to the bath temperature, the heart temperature almost unchanged. Rapid cooling causes a high tensile stress that shrinks the surface layer and is balanced by the heart stress. The increase of temperature gradient increases the tensile stress caused by the initial martensitic transformation, while the increase of the martensite transformation start temperature Ms will cause the surface layer to expand due to the phase transition plasticity, the surface tensile stress will be significantly reduced and transformed into compressive stress, Surface compressive stress is proportional to the amount of surface martensite produced. This surface compressive stress determines whether the heart undergoes martensitic transformation under compressive conditions or, on further cooling, reverses the surface tensile stress. If the martensitic transformation of the heart volume expansion is large enough, and the surface martensite is very hard and brittle, it will make the surface layer due to stress reversal rupture. To this end, the steel surface should appear compressive stress and heart martensitic transformation should occur as late as possible.Strong quenching test and steel quenching performance: The strong quenching method has the advantage of forming compressive stress in the surface, reducing the risk of cracking and improve the hardness and strength. Surface formation of 100% martensite, the steel will be given the largest hardened layer, it can replace the more expensive steel carbon steel, a strong quenching can also promote uniform mechanical properties of steel and produce the smallest distortion of the workpiece . Parts after quenching, the service life under alternating load can be increased by an order of magnitude. [1]Figure 2 strong quenching crack formation probability and cooling rate relationship3 water-air mixture cooling methodBy adjusting the pressure of water and air and the distance between the atomizing nozzle and the surface of the workpiece, the cooling capacity of the water-air mixture can be varied and the cooling can be uniform. Production practice shows that the use of the law on the shape of complex carbon steel or alloy steel parts induction hardening surface hardening, which can effectively prevent the generation of quenching cracks.Figure 3 water-air mixture4 boiling water quenching methodUsing 100 ℃ boiling water cooling, can get a better hardening effect, for quenching or normalizing steel. At present, this technology has been successfully applied to the ductile iron quenching. Taking aluminum alloy as an example: According to the current heat treatment specifications for aluminum alloy forgings and forgings, the quenching water temperature is generally controlled below 60 ° C, the quenching water temperature is low, the cooling speed is high, and a large residual stress after quenching occurs. In the final machining, the internal stress is out of balance due to the inconsistency of the surface shape and size, resulting in the release of residual stress, resulting in deformed, bent, oval and other deformed parts of the machined part becoming irreversible final wastes with serious loss . For example: propeller, compressor blades and other aluminum alloy forging deformation after machining obvious, resulting in parts size tolerance. Quenching water temperature increased from room temperature (30-40 ℃) to boiling water (90-100 ℃) temperature, the average forging residual stress decreased by about 50%. [2]Figure 4 boiling water quenching diagram5 hot oil quenching methodThe use of hot quenching oil, so that the workpiece before further cooling at a temperature equal to or near the temperature of Ms point in order to minimize the temperature difference, can effectively prevent quenching the workpiece distortion and cracking. The small size of the alloy tool steel die cold 160 ~ 200 ℃ in hot oil quenching, can effectively reduce distortion and avoid cracking.Figure 5 hot oil quenching diagram6 Cryogenic treatment methodThe quenched workpiece is continuously cooled from room temperature to a lower temperature so that the retained austenite continues to be transformed into martensite, the purpose of which is to improve the hardness and abrasion resistance of the steel, improve the structural stability and the dimensional stability of the workpiece, and effectively Improve tool life.Cryogenic treatment is liquid nitrogen as a cooling medium for material processing methods. Cryogenic treatment technology was first applied to the wear tools, mold tool materials, and later extended to alloy steel, carbide, etc., using this method can change the internal structure of metal materials, thereby improving the mechanical properties and processing properties, which is currently One of the latest toughening processes. Cryogenic treatment (Cryogenictreatment), also known as ultra-low temperature treatment, generally refers to the material below -130 ℃ for processing to improve the overall performance of the material. As early as 100 years ago, people began to cold treatment applied to watch parts, found to improve the strength, wear resistance, dimensional stability and service life. Cryogenic treatment is a new technology developed on the basis of ordinary cold treatment in the 1960s. Compared with the conventional cold treatment, cryogenic treatment can further improve the mechanical properties and stability of the material, and has a broader application prospect.Cryogenic treatment mechanism: After cryogenic treatment, the residual austenite in the internal structure of the metal material (mainly mold material) is transformed to martensite, and the precipitated carbide is also precipitated in the martensite, so that the martensite can be eliminated In the residual stress, but also enhance the martensite matrix, so its hardness and wear resistance also will increase. The reason for the increase in hardness is due to the transformation of part of the retained austenite into martensite. The increase in toughness is due to the dispersion and small η-Fe3C precipitation. At the same time, the carbon content of the martensite decreases and the lattice distortion decreases, Plasticity improvement.Cryogenic treatment equipment mainly consists of liquid nitrogen tank, liquid nitrogen transmission system, deep cold box and control system. In the application, cryogenic treatment is repeated several times. Typical processes such as: 1120 ℃ oil quenching + -196 ℃ × 1h (2-4) deep cryogenic treatment +200 ℃ × 2h tempering. After the treatment of the organization there has been the transformation of austenite, but also precipitated from the quenched martensite dispersion of highly coherent relationship with the matrix of ultrafine carbides, after subsequent low temperature tempering at 200 ℃, the growth of ultrafine carbides Dispersed ε carbides, the number and dispersion significantly increased. The cryogenic treatment is repeated a number of times. On the one hand, the superfine carbides are precipitated from the martensite transformed from the retained austenite at the time of the previous cryogenic cooling. On the other hand, fine carbides continue to be precipitated in the quenched martensite. Repeated process can make the matrix compressive strength, yield strength and impact toughness increased, improve the toughness of steel, while making the impact wear resistance was significantly improved.Figure 6 cryogenic treatment device schematicSome of the workpiece on the strict size requirements, does not allow processing due to thermal stress caused by excessive deformation, cryogenic treatment should be controlled cooling rate. In addition, in order to ensure the uniformity of the temperature field inside the equipment and reduce the temperature fluctuation, the design of the cryogenic treatment system should take into account the system temperature control accuracy and the rationality of the flow field arrangement. In the system design should also pay attention to meet the less energy consumption, high efficiency, easy operation and other requirements. These are the current development trend of cryogenic treatment system. In addition, some developing refrigeration systems whose refrigeration temperature extends from room temperature to low temperature are also expected to develop into liquid-free cryogenic treatment systems with the decrease of their minimum temperature and the improvement of refrigeration efficiency. [3]References:[1]樊東黎. 強烈淬火——一種新的強化鋼的熱處理方法[J]. 熱處理, 2005, 20(4): 1-3[2]宋微, 郝冬梅, 王成江. 沸水淬火對鋁合金鍛件組織與機械性能的影響[J]. 鋁加工, 2002, 25(2): 1-3[3]夏雨亮, 金滔, 湯珂. 深冷處理工藝及設(shè)備的發(fā)展現(xiàn)狀和展望[J]. 低溫與特氣, 2007, 25(1): 1-3
Source: Meeyou Carbide

First, the molecular beam epitaxial profileIn the ultra-high vacuum environment, with a certain thermal energy of one or more molecules (atoms) beam jet to the crystal substrate, the substrate surface reaction processMolecules in the “flight” process almost no collision with the ambient gas, in the form of molecular beam to the substrate, the epitaxial growth, hence the name.Properties: A vacuum deposition methodOrigin: 20th century, the early 70s, the United States Bell laboratoryApplications: epitaxial growth atomic level precise control of ultra-thin multi-layer two-dimensional structure materials and devices (super-character, quantum wells, modulation doping heterojunction, quantum yin: lasers, high electron mobility transistors, etc.); combined with other processes, But also the preparation of one-dimensional and zero-dimensional nano-materials (quantum lines, quantum dots, etc.).Typical features of MBE:(1) The molecules (atoms) emitted from the source furnace reach the substrate surface in the form of a “molecular beam” stream. Through the quartz crystal film thickness monitoring, can strictly control the growth rate.(2) molecular beam epitaxy growth rate is slow, about 0.01-1nm / s. Can achieve single atomic (molecular) layer epitaxy, with excellent film thickness controllability.(3) By adjusting the opening and closing of the baffle between the source and the substrate, the composition and the impurity concentration of the film can be strictly controlled, and selective epitaxial growth can be achieved.(4) non-thermal equilibrium growth, the substrate temperature can be lower than the equilibrium temperature, to achieve low temperature growth, can effectively reduce the interdiffusion and self-doping.(5) with reflective high-energy electron diffraction (RHEED) and other devices, can achieve the original price observation, real-time monitoring.Growth rate is relatively slow, both MBE is an advantage, but also its lack, not suitable for thick film growth and mass production.Second, silicon molecular beam epitaxy1 basic profileSilicon molecular beam epitaxy includes homogeneous epitaxy, heteroepitaxy.The silicon molecular beam epitaxy is the epitaxial growth of silicon (or silicon-related materials) on a suitably heated silicon substrate by physical deposition of atoms, molecules or ions.(1) during the epitaxial period, the substrate is at a lower temperature.(2) Simultaneous doping.(3) the system to maintain high vacuum.(4) pay special attention to the atomic clean surface.Figure 1 Schematic diagram of the working principle of silicon MBE2 Development history of silicon molecular beam epitaxyDeveloped relative to CVD defects.CVD defects: substrate high temperature, 1050oC, to the doping serious (with high temperature). The original molecular beam epitaxy: the silicon substrate heated to the appropriate temperature, vacuum evaporation of silicon to the silicon substrate, the epitaxial growth.Growth Criteria: The incident molecules move sufficiently to the hot surface of the substrate and are arranged in the form of a single crystal.3 The importance of silicon molecular beam epitaxyThe silicon MBE is carried out in a strictly controlled cryogenic system.(1) can well control the impurity concentration to reach the atomic level. The undoped concentration is controlled at <3 × 1013 / cm3.(2) The epitaxy can be carried out under the best conditions without defects.(3) The thickness of the epitaxial layer can be controlled within the thickness of the single atomic layer, superlattice epitaxy, several nm ~ several tens of nm, which can be designed manually, and the preparation of excellent performance of the new functional materials.(4) Homogeneous epitaxy of silicon, heteroepitaxy of silicon.4 epitaxial growth equipmentDevelopment direction: reliability, high performance and versatilityDisadvantages: high prices, complex, high operating costs.Scope: can be used for silicon MBE, compound MBE, III-V MBE, metal semiconductor MBE is developing.Basic common features:(1) basic ultra-high vacuum system, epitaxial chamber, Nuosen heating room;(2) analysis means, LEED, SIMS, Yang EED, etc .;(3) injection chamber.Figure 2 Schematic diagram of silicon molecular beam epitaxial system(1) electron beam bombardment of the surface of the silicon target, making it easy to produce silicon molecular beam. In order to avoid the radiation of the silicon molecular beam to the side to cause adverse effects, large area screen shielding and collimation is necessary.(2) resistance to heating the silicon cathode can not produce strong molecular beam, the other graphite citrus pots have Si-C stained, the best way is to electron beam evaporation to produce silicon source. Because, some parts of the silicon MBE temperature is higher, easy to evaporate, silicon low evaporation pressure requirements of the evaporation source has a higher temperature. At the same time, the beam density and scanning parameters to control. Making the silicon melting pit just in the silicon rod, silicon rods become high-purity citrus.There are several kinds of monitoring molecular beam:(1) Quartz crystal is often used to monitor beam current, beam shielding and cooling appropriate, can be satisfied with the results, but the noise affects the stability. After several μm, the quartz crystal loses its linearity. Frequent exchange, the main system is often inflated, which is not conducive to work.(2) small ion table, measured molecular beam pressure, rather than measuring the molecular beam flux. Due to the deposition on the system components leaving the standard.(3) low-energy electron beam, through the molecular beam, the use of electrons detected by the excitation fluorescence. The atoms are excited and quickly degrade to the ground state to produce uv fluorescence, and the optical density is proportional to the beam density after optical focusing. Do the feedback control of the silicon source. Inadequate: cut off the electron beam, most of the infrared fluorescence and background radiation will make the signal to noise ratio deteriorated to the extent of instability. It only measured atomic class, can not measure molecular substances.(4) Atomic absorption spectra, monitoring the beam density of doped atoms.With the intermittent beam current, Si and Ga were detected by 251.6nm and 294.4nm optical radiation respectively. The absorption intensity of the beam through the atomic beam was converted into atomic beam density and the corresponding ratio was obtained.Molecular beam epitaxy (MBE) substrate base is a difficult point.MBE is a cold wall process, that is, silicon substrate heating up to 1200 ℃, the environment to room temperature. In addition, the silicon wafer to ensure uniform temperature. Hill resistance refractory metal and graphite cathode, the back of the radiation heating, and the entire heating parts are installed in liquid nitrogen cooled containers, in order to reduce the thermal radiation of the vacuum components. The substrate is rotated to ensure uniform heating. Free deflection, can enhance the secondary implantation doping effect.
Source: Meeyou Carbide

1, Review of Organic Halide Perovskite – related Photoelectric PropertiesFigure 1 Spectral position and PL peakOrganic halide perovskites are widely used in optoelectronics research. Methyl ammonium and formamidine lead iodide as photovoltaics show excellent photoelectric properties and stimulate researchers’ enthusiasm for light-emitting devices and photodetectors. Recently, the University of Toronto Edward H. Sargent (Correspondent) team of organic metal halide perovskite optical and electrical properties of the material were studied. Outlines how material composition and form are associated with these attributes, and how these properties ultimately affect device performance. In addition, the team also analyzed different material properties of the perovskite materials, in particular the bandgap, mobility, diffusion length, carrier lifetime and trap density.The Electrical and Optical Properties of Organometal Halide Perovskites Relevant to Optoelectronic Performance（Adv.Mater.,2017,DOI: 10.1002/adma.201700764）2, Advanced Materials Overview: 2D optoelectronic applications of organic materials Figure 2 Several key steps in the application of two-dimensional organic materialsThe 2D material with atomic thin structure and photoelectron properties has attracted the interest of researchers in applying 2D materials to electronics and optoelectronics. In addition, as a two-dimensional material series of emerging areas, the organic nanostructure assembled into 2D form provides molecular diversity, flexibility, ease of processing, light weight, etc., for optoelectronic applications provides an exciting prospect. Recently, Tianjin University, Professor Hu Wenping, Ren Xiaochen assistant researcher (common newsletter) and others reviewed the application of organic two-dimensional materials in optoelectronic devices. Examples of materials include 2D, organic, crystalline, small molecules, polymers, self- Covalent organic skeleton. The application of 2D organic crystal fabrication and patterning technology is also discussed. Then the application of optoelectronic devices is introduced in detail, and the prospect of 2D material is briefly discussed.2D Organic Materials for Optoelectronic Applications（Adv.Mater.,2017,DOI: 10.1002/adma.201702415）3, Advanced Materials Review: 2D Ruddlesden-Popper Perovskite PhotonicsFigure 3 Schematic diagram of 3D and 2D perovskite structuresThe traditional 3D organic-inorganic halide perovskite has recently undergone unprecedented rapid development. However, their inherent instabilities in moisture, light and calories remain a key challenge before commercialization. In contrast, the emerging two-dimensional Ruddlesden-Popper perovskite has received increasing attention due to its environmental stability. However, 2D perovskite research has just started. Recently, the University of Fudan University, Liang Ziqi (Corresponding author) team published a review first introduced 2D perovskite and 3D control of a detailed comparison. And then discussed the two-dimensional perovskite organic interval cationic engineering. Next, quasi-two-dimensional perovskites between 3D and 2D perovskites were studied and compared. In addition, 2D perovskite unique exciton properties, electron-phonon coupling and polaron are also shown. Finally, a reasonable summary of the structure design, growth control and photophysics research of 2D perovskite in high performance electronic devices is presented.2D Ruddlesden–Popper Perovskites for Optoelectronics（Adv.Mater.,2017,DOI: 10.1002/adma.201703487）4, Science Advances Summary: Lead Halide Perovskite: Crystal-Liquid Binary, Phonon Glass Electronic Crystals and Great Polaron FormationFigure 4 CH3NH3PbX3 perovskite structureLead anodized perovskite has proven to be a high performance material in solar cells and light emitting devices. These materials are characterized by the expected coherent band transport of crystalline semiconductors, as well as the dielectric response and phonon dynamics of the liquid. This “crystal-liquid” duality means that lead halide perovskites belong to phonon glass electron crystals – a class of thermoelectric materials that are considered to be the most efficient. Recently, the University of Columbia Zhu Xiaoyang (communication author) team reviewed the crystal-liquid duality, the resulting dielectric response responsible for the formation and selection of carrier polaron, which causes perovskite with defect tolerance, moderate Of the carrier mobility and the combined performance of the radiation. Large polaron formation and phonon glass characteristics can also explain the significant reduction in carrier cooling rates in these materials.Lead halide perovskites: Crystal-liquid duality, phonon glass electron crystals, and large polaron formation（Sci. Adv.,2017,DOI:10.1126/sciadv.1701469）5, Progress in Polymer Science Review: Lithography of silicon-containing block copolymersFig.5 Melt phase diagram of diblock copolymerRecently, the National Tsinghua University Rong-Ming Ho (Correspondent) and others published a summary of the different methods through the preparation of ordered block copolymer (BCP) film the latest progress, focusing on the use of silicon-containing BCP as lithography applications. With the advantages of Si-containing blocks, these BCPs have smaller feature sizes due to their high resolution, large segregation intensity and high etch contrast. Considering that poly (dimethylsiloxane) (PDMS) has been extensively studied in Si-containing BCPs, the possibility of photolithography using PDCP-containing BCP has been demonstrated through previous and ongoing studies. Subsequent sections detail the main results of the DSA approach. The new trend of lithographic printing application and the application of photolithography nano – pattern using silicon – containing BCPs are also discussed. Finally, the conclusion and prospect of BCP lithography are introduced.Silicon-Containing Block Copolymers for Lithographic Applications（Prog. Polym. Sci.,2017,DOI:10.1016/j.progpolymsci.2017.10.002）6, Angewandte Chemie International Edition Overview: CH3NH3PbI3 perovskite solar cell theoretical studyFigure 6 Electronic density patternPower conversion efficiency (PCEs) of more than 22% of the hybridized perovskite perovskite solar cells (PSCs) has attracted considerable attention. Although perovskite plays an important role in the operation of PSCs, the basic theory associated with perovskite remains unresolved. Recently, Professor Xun Nining (Communication Author) of Xi’an University of Architecture and Technology, according to the first principle, evaluated the existing theory of structure and electronic properties, defects, ion diffusion and transfer current of CH3NH3PbI3 perovskite, and ion transport Influence on PSC Current – Voltage Curve Hysteresis. The moving current associated with the possible ferroelectricity is also discussed. And emphasizes the benefits, challenges and potential of perovskite for PSCs.Theoretical Treatment of CH3NH3PbI3 Perovskite Solar Cells（Angew. Chem. Int. Ed.,2017,DOI: 10.1002/anie.201702660）7, Chemical Society Reviews Overview: Reductive Batteries for Electromechanical Active Materials for Molecular EngineeringFigure 7 Molecular engineering for redox substances for sustainable RFBAs an important large energy storage system, redox batteries (RFBs) have high scalability and independent energy and power control capabilities. However, conventional RFB applications are subject to performance and limitations on high cost and environmental issues associated with the use of metal-based redox substances. Recently, the University of Texas at Austin Guihua Yu (communication author) team proposed the design of these new redox substances system molecular engineering program. The article provides a detailed synthesis strategy for modifying organometallic and organometallic redox substances in terms of solubility, oxidation-reduction potential and molecular size. And then introduced recent advances covering the reaction mechanism of the redox species classified by its molecular structure, the specific functionalization methods and electrochemical properties. Finally, the author analyzes the future development direction and challenge of this emerging research field.Molecular engineering of organic electroactive materials for redox flow batteries （Chem.Soc.Rev.,2017,DOI: 10.1039/C7CS00569E）8, Chemical Society Reviews Overview: Atomic level for energy storage and conversion Non-layered nanomaterialsFigure 8 Atomic-grade layered and non-layered nanomaterialsSince the discovery of graphene, the two-dimensional nanomaterials with large atomic thickness and large lateral dimension are highly studied because of their high specific surface area, heterogeneous electronic structure and attractive physical and chemical properties. Recently, Wulonggong University Dushi University academician (communication author) team comprehensively summed up the atomic thickness of non-layered nano-materials preparation method, studied its heterogeneous electronic structure, the introduction of electronic structure operation strategy, and outlined its energy storage and conversion Applications, with particular emphasis on lithium-ion batteries, sodium ion batteries, oxygen, CO2 reduction, CO oxidation reaction. Finally, based on the current research progress, put forward the future direction – in practical application to enhance the performance and new features to explore.Atomically thin non-layered nanomaterials for energy storage and conversion （Chem.Soc.Rev.,2017,DOI:10.1039/C7CS00418D）9, Chemical Reviews Overview: Electrochemical Applications in the Synthesis of Heterocyclic StructuresFigure 9 Mechanism of electro-induced cationic chain reactionThe heterocycle is one of the largest organic compounds to date, and the preparation and transformation of heterocyclic structures have been of great interest to organic chemistry researchers. Various heterocyclic structures are widely found in biologically active natural products, organic materials, agrochemicals and drugs. When people notice that about 70% of all drugs and agrochemicals have at least one heterocycle, people can not ignore them importance. Recently, Professor Zeng Chengchao of Beijing University of Technology (Correspondent Author) team reviewed the progress of electrochemical construction of heterocyclic compounds published by intramolecular and intermolecular cyclization since 2000.Use of Electrochemistry in the Synthesis of Heterocyclic Structures（Chem. Rev.,2017,DOI:10.1021/acs.chemrev.7b00271）
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First, the development of a brief historyThe first stage: 1945 to 1951, the invention of nuclear magnetic resonance and lay the theoretical and experimental basis of the period: Bloch (Stanford University, observed in the water proton signal) and Purcell (Harvard University, observed in the paraffin proton signal) obtained Nobel bonus.The second stage: 1951 to 1960 for the development period, its role by chemists and biologists recognized, to solve many important problems. 1953 appeared in the first 30MHz nuclear magnetic resonance spectrometer; 1958 and early in the emergence of 60MHz, 100MHz instrument. In the mid-1950s, 1H-NMR, 19F-NMR and 31P-NMR were developed.The third stage: 60 to 70 years, NMR technology leap period. Pulse Fourier transform technology to improve the sensitivity and resolution, can be routinely measured 13C nuclear; dual frequency and multi frequency resonance technology;The fourth stage: the late 1970s theory and technology development mature.1,200, 300, 500 MHz and 600 MHz superconducting NMR spectrometers;2, the application of a variety of pulse series, in the application made important development;3, 2D-NMR appeared;4, multi-core research, can be applied to all magnetic cores;5, there have been “nuclear magnetic resonance imaging technology” and other new branch disciplines.Second, the main purpose:1. Determination and confirmation of the structure, and sometimes can determine the configuration, conformation2. Compound purity inspection, the sensitivity of thinner, paper chromatography high3. Mixture analysis, such as the main signal does not overlap, without separation can determine the proportion of the mixture.4. Proton exchange, the rotation of a single bond, the transformation of the ring and other chemical changes in the speed of the presumption1. the spin of the nucleusOf the isotopes of all elements, about half of the nuclei have spin motion. These spin nuclei are the object of nuclear magnetic resonance. Spin Quantum: The number of quantum numbers describing the spin motion of the nucleus, which can be an integer, a half integer, or a zero.In the organic compound composition elements, C, H, O, N is the most important element. In its isotopes, 12C, 16O are non-magnetic and therefore do not undergo nuclear magnetic resonance. 1H natural abundance of large, strong magnetic, easy to determine, so the NMR study was mainly for the proton. 13C abundance is small, only 12C 1.1%, and the signal sensitivity is only a proton to get 1/64. So the total sensitivity of only 1/6000 of 1H, more difficult to determine. But in the past 30 years, nuclear magnetic resonance instrument is greatly improved, can be measured in a short time 13C spectrum, and give more information, has become the main means of NMR. 1H, 19F, 31P natural abundance of large, strong magnetic, and nuclear charge distribution of spherical, the most easy to determine.2. Nuclear magnetic resonance phenomena① Precession: Spin with a certain magnetic moment Under the action of external magnetic field H0, this core will form angle for the kinematic motion: is the precession kinematic velocity, which is proportional to H0 (external magnetic field strength).② spin nuclear in the external magnetic field orientation: no external magnetic field, the spin magnetic orientation is chaotic. The magnetic core is in the external magnetic field H0, with (2I + 1) orientation. The spin of the magnetic core in the external magnetic field can be analogous to the precession (pronation, swing) of the gyroscope in the gravitational field.③ conditions of nuclear magnetic resonanceThe magnetic resonance magnetic field must have the magnetic nuclei, the external magnetic field and the RF magnetic field. The frequency of the RF magnetic field is equal to the precession frequency of the spin nucleus, and the resonance occurs from the low energy state to the high energy state.④ nuclear magnetic resonance phenomenon:In the vertical direction of the external magnetic field H0, a rotating magnetic field H1 is applied to the precession nucleus. If the rotational frequency of H1 is equal to the rotational precession frequency of the nucleus, the precession nucleus can absorb energy from H1 and transition from low energy state to high energy state Nuclear magnetic resonance.3. Saturation and relaxationLow energy nuclear is only 0.001% higher than high energy nuclear. Therefore, the low energy state core is always more than the high energy nuclear, because such a little surplus, so can observe the absorption of electromagnetic waves. If the nuclear continuous absorption of electromagnetic waves, the original low energy state is gradually reduced, the intensity of the absorption signal will be weakened, and ultimately completely disappeared, this phenomenon is called saturation. When saturation occurs, the number of cores in the two spin states is exactly the same. In the external magnetic field, the low-energy nuclei are generally more nuclear than the high-energy state, absorb the electromagnetic wave energy and migrate to the high-energy state of the core will be released by a variety of mechanisms of energy, and return to the original low energy state, this process called relaxation.4. Shield effect – chemical shift① ideal state of resonanceFor isolated, bare nuclei, ΔE = (h / 2π) γ · H;Under certain H0, a nucleus has only one ΔEΔE = E outside = hνOnly the only frequency ν of absorptionSuch as H0 = 2.3500T, 1H absorption frequency of 100 MHz, 13C absorption frequency of 25.2 MHz② real core: shielding phenomenonNuclear outside the electron (not isolated, not exposed)In the compounds: the interatomic binding (role) is different, such as chemical bonds, hydrogen bonds, electrostatic interactions, intermolecular forcesImagine: In H0 = 2.3500 T, due to the outer electrons of the shield, in the nuclear position, the real magnetic field is slightly smaller than 2.3500 TResonance frequency slightly higher than 100 MHzHow much is it? 1H is 0 to 10, and 13C is 0 to 250The hydrogen nuclei have electrons outside, and they repel the magnetic field lines of the magnetic field. For the nucleus, the surrounding electrons are shielded (Shielding) effect. The greater the density of the electron cloud around the core, the greater the shielding effect, the corresponding increase in magnetic field strength to make it resonant. The electron cloud density around the nucleus is affected by the connected groups, so the nuclei of different chemical environments, they suffer from different shielding effects, their nuclear magnetic resonance signals also appear in different places.③ If the instrument is measured with a 60MHz or 100MHz instrument, the electromagnetic wave frequency of the organic compound proton is about 1000Hz or 1700Hz. In determining the structure, the need to determine the correct resonant frequency, often requires several Hz accuracy, generally with the appropriate compound as the standard to determine the relative frequency. The difference between the resonant frequency of the standard compound and the resonant frequency of a proton is called the chemical shift.5. H NMR spectroscopy informationThe number of signals: how many different types of protons are present in the moleculeThe position of the signal: the electronic environment of each proton, the chemical shiftThe intensity of the signal: the number or number of each protonSplit situation: how many different protons are presentThe chemical shift of common types of organic compounds① induced effect② conjugate effectThe conjugation effect is weak or enhanced by proton shielding due to the displacement of the π electrons③ anisotropic effectIt is difficult to explain the chemical shift of H with respect to pi-electrons, and it is difficult to explain the electronegativity④ H key effectROH, RNH2 in 0.5-5, ArOH in 4-7, the range of change, the impact of many factors; hydrogen bonding with temperature, solvent, concentration changes significantly, you can understand the structure and changes related to hydrogen bonds.⑤ solvent effectBenzene forms a complex with DMF. The electron cloud of the benzene ring attracts the positive side of the DMF, rejecting the negative side. α methyl is in the shielding region, the resonance moves to the high field; and β methyl is in the masking region, the resonance absorption moves to the low field, and the result is that the two absorption peak positions are interchanged.
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