Stage analysis of mold densification process
According to the principle of powder metallurgy, the hot pressing and sintering process of diamond bits is a comprehensive process including diffusion, flow and physical and chemical reaction under pressure pressure at high temperature.
The process of densification of product (fetus) can be divided into three stages:
1) stage of rapid densification.In the mold, the powder material is basically in the state of loose loading. At the initial stage of hot pressing, the particles slide relatively, break and plastic deformation, and the compaction rate is high. In this stage, the hot pressing pressure plays an important role.
2) densification deceleration stage.As the temperature rises, the water and other volatile substances absorbed by the mold and powder become volatile, and a large number of active atoms gradually appear on the surface of the powder. The activation amount on the atomic surface decreases, thus preparing for sintering reaction.When the temperature rises below a certain temperature at the melting point of the bonding phase, the holding period.
On the one hand, the inhomogeneity caused by the rapid temperature rise in all parts of the mold can be balanced, and the ultra-low temperature screw unit can eliminate the stress in the tire body.On the other hand, a large number of defects such as vacancy, dislocation, internal stress, distortion, and surface performance energy in powder particles are released to make full preparation for further sintering. At the same time, the liquid phase quantity of the metal bonded at a low melting point is controlled to enable the bit to enter a pre-sintering state.
3) reaching the ultimate density phase with the final temperature rise again to the sintering temperature, liquid volume increased significantly, the powder body under the action of liquid surface tension move to permutation and combination, as a result of the atomic vibration amplitude increase, diffusion, there are more atoms in the scope of the atomic force into tables grain boundary to low grain interface, and with the expanding of the grain interface, the sintering intensity increases.