Powder metallurgy is the technology of producing metal materials, composite materials and various types of products using metal powder as raw material after forming and sintering. Powder metallurgy methods are somewhat similar to the production of ceramics, therefore, a series of new powder metallurgy techniques can also be used to prepare ceramic materials.
Due to the advantages of powder metallurgy technology, it has become the key to solving the problem of new materials and plays a key role in the development of new materials. Many factors affect the properties of sintered bodies, namely powder properties, molding and sintering conditions. Factors of sintering conditions include heating rate, sintering temperature and time, cooling rate, sintering atmosphere and pressure conditions.
The sintering temperature and time can affect the porosity, density, strength and hardness of the sintered body. High sintering temperature and long heating time will reduce product performance and even lead to product scorch defects, while low sintering temperature or long heating time may cause performance degradation due to the sintering process.
The sintering atmosphere usually used in powder metallurgy is a reducing atmosphere, vacuum, hydrogen atmosphere, etc.; the sintering atmosphere directly affects the properties of the sintered body; sintering in a reducing atmosphere can prevent the burning of the compact and allow the reduction of surface oxides. For example, iron and copper-based products are typically decomposed using gas or ammonia, while cemented carbide and stainless steel typically use pure hydrogen. Active metals or refractory metals (eg beryllium, titanium, zirconium, tantalum), cemented carbides containing Tic alloys and stainless steels can be used for vacuum sintering.
If two or more components are present in the powder compact, sintering may occur above the melting points of the components, resulting in a small liquid phase in the powder compact. Pressure is applied to the powder during sintering to facilitate the densification process. Sometimes pressure sintering and hot pressing are synonymous, but hot pressing refers to the process of obtaining a product directly after powder molding and sintering.
At the same time, while improving the performance of the sintered body, some physical or chemical measures are also used to significantly reduce the sintering temperature and reduce the sintering time. When the powder is introduced into the compaction process, a direct current (DC) and pulsed power are passed and then an electric arc is created between the powder particles. Then the sintering process begins. During the sintering process, pressure is gradually added to the workpiece, thereby combining the forming and sintering of the two processes.