欧美人妻精品一区二区三区99,中文字幕日韩精品内射,精品国产综合成人亚洲区,久久香蕉国产线熟妇人妻

The so-called powder metallurgy method is to make a powder of the raw material of the alloy to be produced, and then mix the powders in an appropriate amount and pressurize and solidify into a certain shape. These powder pieces will be placed in a reducing atmosphere (for example, hydrogen), heated and sintered to form an alloy. This is a metallurgical method that is completely different from the previous casting method.
The sintering referred to herein can be simply defined as the promotion of agglomeration of metal crystal grains by the action of pressurization and warming. We apply a certain amount of pressure to the powder with the alloy composition to compact it. At high temperatures, the intimately contacted powders stick to each other and gradually fill the voids to form a high density alloy. The heating temperature at this time is the melting temperature of the low melting component in the alloy component. Thus, the alloy ingot is sintered at a temperature below the melting point of the entire powder component. This method is similar to the method of combining the two processes of smelting and casting, and its properties are close to those of cast alloys. But from a metallographic point of view, it should be a branch of alloy castings.
Cemented carbide is manufactured by this powder metallurgy method. Generally, powders such as tungsten, carbon, cobalt, titanium, and cerium are used for batch mixing, and then pressed and sintered to form an alloy. Thus, the product of this metallurgical process is also referred to as a sintered cemented carbide or a cemented carbide alloy. In recent years, powder metallurgy methods have developed very rapidly. Cemented carbides, oil-bearing alloys, electrical contacts, metal bonded diamond wheels, and special decorative metal products are all manufactured by this powder metallurgy method.
For example, the pressed semi-finished product of 30 mm in length is now heated to 1000-1400 ° C. The volume change of the pressed product at about 30 ° C for about 5 minutes is shown in Figure 2-2. Shrinkage generally begins at 1150 ° C. In the case of 6% Co, the shrinkage proceeds very regularly, ending at approximately 1320 ° C. In the case of 10% Co, at 1180-1200 ° C, the contraction is temporarily interrupted. As the temperature continues to rise, the shrinkage proceeds rapidly, and when the temperature reaches 1300 ° C, it tends to balance.

The Principle of Powder Sintering in Metallurgy 1

Thereafter, since the number of contact points of the particles and the contact area is remarkably increased, each of the particles is in a state of easily releasing excess energy (free energy) held by itself. Thus, from about 200 ° C, cobalt begins to diffuse, at which point the first stage of sintering begins. When the temperature rises again, β-Co is converted to γ-Co at around 490 °C. At 600 ° C, carbon begins to diffuse into the cobalt and becomes a mass solution. The finer the tungsten carbide particles, or the better the cobalt-coated tungsten carbide, the faster this diffusion phenomenon will occur. This diffusion has the same effect as applying strong compressive pressure to the compact. However, during the temperature rise, almost no liquid phase is observed at this temperature.
However, near this temperature, the bending strength is significantly increased. Usually, a hardness alloy of 6% cobalt is sintered at a temperature of about 1400 ° C. At this temperature, WC gradually dissolves into the liquid phase, and particularly fine WC dissolves rapidly, and the large WC has large surface energy due to the sharp corner portion. It is round after being dissolved. As a result, the liquid phase portion becomes more and more, and as the reaction progresses toward the direction in which the free energy decreases, the alloy shrinks and the pores gradually decrease. On the other hand, in the portion where the tungsten carbide particles are in contact with each other, the phenomenon of volume diffusion, particularly surface diffusion, continues to occur. There is also the possibility that carbide particles will bond with each other. Further, WC may also locally precipitate from the liquid phase at a portion where the tungsten carbide contacts each other. As a result, various reasons have prompted the growth of tungsten carbide grains, resulting in a dense alignment. However, the temperature is further increased, and when it exceeds 1600 ° C, gas is generated inside the product, causing expansion of the crystal arrangement. It is said that the gas is generated by the presence of impurities such as SiO2. On the contrary, if the temperature is lowered, the WC particles dissolved in the liquid phase are precipitated on the WC particles having small surface energy. Even after the liquid phase disappears into a solid state, the tungsten carbide continues to separate until only 1% remains.

The Principle of Powder Sintering in Metallurgy 2

During the sintering process, the tungsten carbide present in the form of a melt in the cobalt moves a small distance and is bonded to the undissolved tungsten carbide, so that uneven structure such as a cast alloy is not formed. The steel containing a large amount of pearlite is aged and hardened by the precipitation of the carbon melt of the alpha iron. In contrast, during the sintering process, the WC particles act as effective nucleation, so there is no age hardening phenomenon, so that the structure is uniform and very stable, not sensitive to heat treatment, and the hardness does not change even at relatively high temperatures. Figure 2-3 shows the high-temperature hardness of tool steel, high-speed steel, cast alloy, stellite alloy (Co-Cr-W), and WC+Co cemented carbide.

Bir cevap yaz?n

E-posta hesab?n?z yay?mlanmayacak. Gerekli alanlar * ile i?aretlenmi?lerdir

骚逼嫩鸡巴喷水视频| 国产无码久久久久久| 久久精品国产自清天天线| 日韩午夜资源在线观看| 中文字幕欧美人妻在线| 97超视频免费在线观看| 尤物AV无码国产在线看| 亚洲欧洲日本精品| 五月天国产成人免费视频| 啊啊啊男女激情插插视频| 黄色av手机在线观看| 美女日比视频播放| 中文国产成人精品久久久| 黑丝美女被操哭边操边尿| 大逼女人污污视频| 黑人妖大鸡吧操逼| 女生小穴色色视频| 青青视频在线人视频在线| 国产污污污在线观看视频| 最新AV中文字幕在线看| 欧美精品第一区二区三区| 高清无码精品一区二区三区| 久久噜噜噜久久熟女精品| ai换脸久久一区二区亚洲av| 我要操死你逼视频| 日本十八禁大骚逼| 91秦先生全集在线观看| 国产又粗又猛又色又免费| 亚洲日韩不卡一区二区三区| 美女亚洲福利视频| 大香蕉中码手机在线视频| 日本免费精品一区二区三区四区| 猛哥操女人B视频| 啊灬啊别停灬用力啊男男在线观看| 黑大吊肏小騷逼噴水| 无码人妻精品一区二区三区蜜桃| 日本成人在线一区中文字幕| 夫妻性生活视频在线直播| 熟妇丰满大阴户熟妇啪啪| 日韩欧美一区二三区风间由美| 国产成人AV一区二区在线观看|