Powder metallurgy is a technology using metal powder (or a mixture of metal powder and non metal powder) as raw materials to produce metal materials, composite products, and various types of products after forming and sintering. Powder metallurgic method is somewhat similar to the production of ceramic; therefore, a series of new powder metallurgy technologies can also be used for the preparation of ceramic materials. Due to the advantages of powder metallurgy technology, it has become the key to solving new materials problem, and plays a pivotal role in the development of new materials.
There are numerous factors affecting the performance of the sintered body, namely traits of powder body, molding and sintering conditions. Factors of sintering conditions include heating rate, sintering temperature and time, cooling rate, sintering atmosphere and pressure conditions.
Temperature and Time of Sintering
Sintering temperature and length of time can influence the porosity, density, strength and hardness of the sintered body. The high sintering temperature and long heating time will reduce product performances, or even lead to burnt defects in products, while low sintering temperature or short long heating time might cause performance degradation owing to under-sintering.
Sintering atmosphere conventionally applied in powder metallurgy is reducing atmosphere, vacuum, hydrogen atmosphere and the like. Sintering atmosphere directly affects the performance of the sintered body. Sintering in a reducing atmosphere can prevent from burning of the compacts and allow the reduction of surface oxides. For example, iron and copper based products often use gas or decomposition of ammonia, while cemented carbides and stainless steel usually utilize pure hydrogen. Reactive metal or refractory metal (e.g., beryllium, titanium, zirconium, tantalum), cemented carbides containing Tic alloy and stainless steel can be used for vacuum sintering. Vacuum sintering can avoid the adverse effects of harmful components (H2O, O2, H20) and lower the sintering temperature (generally lower 100 ~ 150 centigrade) as well.
Methods of Powder Metallurgy Sintering
If there are two or more components in powder compacts, sintering might happen above the melting point of a component and thus leading to the occurrence of a small amount of liquid phase in powder compacts.
Apply pressure to the powder body while sintering so as to promote densification process. Sometimes pressure sintering and hot pressing are synonymous, but hot pressing refers to the process of getting products directly after the powder is shaped and sintered together.
It is a method of using some physical or chemical measures to reduce the sintering temperature and reduce sintering time significantly as well while improving and enhancing the performance of the sintered body at the same time.
Pass direct current (DC) and pulse power through when the powder is introduced into the compacting process, then arcs will be generated between powder particles. Afterwards starts the sintering process. While sintering, add pressure gradually to the work piece so as to combine forming and sintering these two processes together.
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