Views: 0 Author: Site Editor Publish Time: 2022-12-16 Origin: Site
Vacuum hot press furnace: A process in which a loose powder placed in a mold of a defined
shape or a powder compact is heated and pressure is applied at the same time so that
the material is formed and sintered at the same time in a vacuum environment.
The first stage: pore connectivity
Including early and middle sintering stage. The pressure causes plastic bending service in the particle contact area.
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 sliding by climbing. The density of sintered body increases rapidly.
The second stage: hole isolation
Also known as sintering stage. The pores are located at the grain boundary and
the micropores in the grain are not excluded. At this time, the mechanism of the primary stage still exists,
but creep and diffusion become the main mechanism of sintering, the material shrinkage is slow, the product densification degree is high.
Hot pressing sintering densification process
At the later stage of sintering, the pressure of closed pores increases,
which cancels out the effect of surface tension and weakens the grain boundary diffusion,
while the volume diffusion rate is slow, which makes the shrinkage difficult at the later stage.
Hot pressing can provide an external force to compensate for the offset surface tension and promote 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.