Advantages of vacuum hot pressing furnace and densification process decomposition of hot pressing sintering

The vacuum hot press furnace is a kind of process in which the loose powder placed in the mold with the limited shape or the powder pressing blank is heated and the pressure is applied at the same time to make the material forming and sintering complete at the same time. It is mainly used to improve the performance of powder and non-metallurgical products. Applicable materials include metal matrix composites and various target materials.

Advantages of vacuum hot pressing sintering

1, hot pressing, the powder is in a thermoplastic state, deformation resistance is small, the required molding pressure is small.

2. Due to the simultaneous heating and pressurization, it is helpful for the contact, diffusion and flow mass transfer of powder particles, which can reduce the sintering temperature and shorten the sintering time, thus inhibiting the grain growth.

3. Hot pressing sintering is completed under vacuum condition, and the sintered body has low porosity, high densification degree and fine grain, and the mechanical and electrical properties of the product are good.

The decomposition was carried out by hot pressing sintering densification process in vacuum hot pressing furnace

First, sintering stage: pore connectivity

Including early and middle sintering stage. Plastic yield occurs in the contact zone of particles due to pressure. Power exponential creep occurs in the expanded contact zone, which leads to material migration. Volume diffusion and grain boundary diffusion occur between atoms and vacancies: dislocation also causes grain boundary slip by climbing. The density of sintered body increased rapidly.

Two, sintering stage: hole isolation

The pores are located at the product boundary, and the micropores in the grain are not excluded. At this time, the pre-sintering mechanism still exists, but creep and diffusion become the main mechanism of sintering, the material shrinkage is slow, the product densification degree is high. At the later stage of sintering, the pressure of closed pores increases, which cancels out the effect of surface tension, and the grain boundary diffusion is weakened, while the volume diffusion rate is slow, which makes it difficult to shrink at the later stage. Hot pressing can provide external driving force to compensate the offset surface tension and promote the sintering to continue. Under the condition of hot pressing, the solid powder may exhibit the properties of non-Newtonian fluid. When the shear stress exceeds the yield point, the flow will occur, resulting in the increase of mass transfer speed, and the closed pores can be eliminated through the viscous or plastic flow of the material.

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