The basic processes of powder metallurgy are:
1. Preparation of raw material powder. The existing pulverizing methods can be roughly divided into two categories: mechanical method and physicochemical method. The mechanical method can be divided into: mechanical crushing and atomization method; the physical and chemical method can be divided into: electrochemical corrosion method, reduction method, reduction-chemical method, reduction-chemical method, vapor deposition method, liquid deposition method and electrolysis method. Among them, reduction, atomization and electrolysis are the most widely used methods.
2. The powder is formed into the blank of the desired shape. The purpose of forming is to produce compacts of certain shape and size, and to make them have certain density and strength. The forming methods are basically divided into pressure forming and non-pressure forming. Compression moulding is the most widely used in pressure moulding. In addition, the technology of 3D printing can be used to produce embryo lumps.
3. Sintering of billets. Sintering is a key process in powder metallurgy process. The formed compacts are sintered to obtain the required final physical and mechanical properties. Sintering can be divided into unit system sintering and multicomponent system sintering. For solid phase sintering of unit system and multicomponent system, the sintering temperature is lower than the melting point of metal and alloy used; for liquid phase sintering of multicomponent system, the sintering temperature is generally lower than the melting point of refractory component, but higher than the melting point of fusible component. In addition to ordinary sintering, there are also some special sintering processes, such as loose-packed sintering, melt-immersion, hot-pressing and so on.
4. Post-processing of products. After sintering, various methods can be adopted according to the different requirements of products. Such as finishing, oil immersion, machining, heat treatment and electroplating. In addition, in recent years, some new processes such as rolling and forging have also been applied to the sintering process of powder metallurgical materials, and satisfactory results have been achieved.
