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Metal powder vacuum sintering technology
Powder metallurgy is a technology that uses metal powder as a raw material to produce metal materials, composite materials and various types of products after forming and vacuum sintering.
The powder metallurgy process mainly includes powder pretreatment, powder compaction, powder vacuum sintering, post-treatment and other links. Among them, powder vacuum sintering is a high-temperature treatment process that further combines compacts or loose powder bodies in a vacuum environment to improve strength and other properties.
Metal powder vacuum sintering process
Powder sintering is a process of reducing the free energy of the system, which is manifested as the flattening of the sintering neck and particle surface, the reduction of the total surface area and surface energy of the system, the reduction of the total volume and total surface area of voids, and the elimination of lattice distortion within the grain.
The powder vacuum sintering process is formed by the coupling of surface diffusion, viscous flow, evaporation condensation, volume diffusion and grain boundary diffusion. Among them, the main diffusion mechanism from the initial contact of the powder to the formation of the sintering neck is surface diffusion, the growth stage of the sintering neck is mainly based on volume diffusion, and the shrinkage of pores is mainly based on volume diffusion and vacancy diffusion.
Vacuum sintering of powder particles is divided into three stages: (1) particle bonding (initial stage): the particles change from point contact or surface contact to crystal bonding, forming a sintering neck with a certain strength, resulting in increased strength and conductivity; 2) Sintering neck growth stage (middle stage): The sintering neck grows up through atomic diffusion between particles, forming a connected network structure, the distance between particles decreases, and the overall porosity decreases; (3) Spheroidization of closed cells And shrinking stage (late stage): Most of the pores are closed pores, and the number increases, and the sintered body shrinks slowly, mainly due to the reduction and shrinkage of closed pores.
Factors Affecting the Quality of Metal Powder Vacuum Sintering
There are many factors that affect the performance of sintered body, including powder characteristics, molding and vacuum sintering conditions. Factors of vacuum sintering conditions include heating rate, vacuum sintering temperature and time, cooling rate, sintering atmosphere and pressure conditions.
The vacuum sintering temperature and time can affect the porosity, density, strength and hardness of the sintered body. High vacuum sintering temperature and long heating time will reduce product performance and even cause product burnt 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 reducing atmosphere, vacuum, hydrogen atmosphere, etc.; the sintering atmosphere directly affects the performance of the sintered body; sintering in a reducing atmosphere can prevent the burning of the compact and allow the reduction of the surface oxide.
For example, iron and copper based products are usually decomposed using gas or ammonia, while cemented carbide and stainless steel usually use pure hydrogen. Reactive metals or refractory metals (such as beryllium, titanium, zirconium, tantalum), cemented carbides containing TiC alloys and stainless steel can be used for vacuum sintering.
With the gradual development and maturity of materials, equipment, molds, processes, and automation technologies, powder metallurgy has become more and more widely used, and has become a new industrial technology that has attracted much attention in consumer electronics, automobiles, and other industries.
Selection of metal powder vacuum sintering furnace: powder metallurgy vacuum sintering furnace produced by SIMUWU company is used for Sm-Co, AlNiCo, metal mesh, hard alloy, ceramic material, photoelectric coating material, graphite purification, magnet material and rare refractory metal, alloy (Tungsten, Mo, W-Cu alloy) vacuum sintering process, also supports atmosphere sintering. The highest temperature can reach 2200C. The vacuum furnace control system is controlled by PLC, and the temperature is controlled by an intelligent temperature controller, with accurate control and high degree of automation. User selectable automatic or manual bumpless switching operation.
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