Metal Powder Sintering Technology

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Powder sintering is a process of reducing the free energy of the system, which is manifested by the flattening of the sintering neck and the surface of the particles, the reduction of the total surface area and surface energy of the system, the reduction of the total void volume and the total surface area, and the elimination of lattice distortion in the grains. The powder sintering process is formed by the coupling of surface diffusion, viscous flow, evaporation and condensation, volume diffusion and grain boundary diffusion. The main diffusion mechanism for the formation of the powder from the initial contact with the sintering neck is surface diffusion. The growth stage of the sintering neck is dominated by volume diffusion, and the shrinkage of pores is dominated by volume diffusion and vacancy diffusion.

 The Basic Process of Powder Metallurgy:

Pulverizing: Pulverizing is the process of making raw materials into powder. Commonly used methods of making powder include oxide reduction method and mechanical method.

Mixing: Mixing is the process of mixing various required powders in a certain proportion and homogenizing them to make green powder. There are three types: dry type, semi-dry type and wet type, which are used for different requirements.

Forming: Forming is the process of putting a uniformly mixed mixture into a press mold and pressing it into a parison with a certain shape, size and density. The molding method is basically divided into pressure molding and pressureless molding. Compression molding is most widely used in compression molding.

Sintering: Sintering is a key process in the powder metallurgy process. The formed compact is sintered to obtain the required final physical and mechanical properties. Sintering is divided into unit system sintering and multi-system sintering. In addition to ordinary sintering, there are also special sintering processes such as loose sintering, immersion method, and hot pressing method.

Post-processing: After sintering, various methods can be adopted according to different product requirements. 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 processing of powder metallurgy materials after sintering, and have achieved ideal results. There are many factors that affect the performance of the sintered body, including the characteristics of the powder, molding and sintering conditions. The 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 cause product scorch defects. At the same time, low sintering temperature or long-term heating may cause performance degradation due to the sintering process.

The sintering atmosphere commonly used in powder metallurgy is reduced atmosphere, vacuum, hydrogen atmosphere, etc.; the sintering atmosphere directly affects the performance of the sintered body; sintering in a reducing atmosphere can prevent the combustion of the compact and allow the reduction of surface oxides. For example, iron and copper-based products usually use gas or ammonia to decompose, while cemented carbide and stainless steel usually use pure hydrogen. Active metals or refractory metals (such as beryllium, titanium, zirconium, tantalum), hard alloys containing TiC alloys and stainless steel can be used for vacuum sintering.

Shanghai Geheng Vacuum Technology Co., Ltd. is a vacuum heat treatment furnace manufacturer with many years of experience in design, manufacturing and production. Mainly produce vacuum heat treatment furnace, vacuum sintering furnace, vacuum brazing furnace, New Energy And Environmental Protection Equipment and other vacuum equipments.Provide customized services, equipment work area can be based on customer output.

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