The cemented carbide sintering process can be divided into four basic stages as follows:
1. In the stage of removing the forming agent and pre-sintering, the sintered body undergoes the following changes at this stage:
1) Removal of the molding agent, with the increase of temperature in the initial stage of sintering, the molding agent gradually decomposes or vaporizes, and the sintered body is excluded. The type and amount of molding agent and the sintering process vary.
2) The oxides on the surface of the powder are reduced. At the sintering temperature, hydrogen can reduce the oxides of cobalt and tungsten. If the forming agent is removed in vacuum and sintered, the carbon-oxygen reaction is not strong.
3) The contact stress between powder particles is gradually eliminated, the bonding metal powder begins to recover and recrystallize, surface diffusion begins to occur, and the strength of the compact is improved.
2. Solid-phase sintering stage (800℃--eutectic temperature); at the temperature before the liquid phase, in addition to continuing the process of the previous stage, the solid-phase reaction and diffusion are intensified, the plastic flow is enhanced, and the sintered body appears obviously contraction.
3. Liquid phase sintering stage (eutectic temperature - sintering temperature); when the sintered body appears in the liquid phase, the shrinkage is completed quickly, and then the crystalline transformation occurs to form the basic structure and structure of the alloy.
4. Cooling stage (sintering temperature - room temperature); in this stage, the structure and phase composition of the alloy have some changes with different cooling conditions. This feature can be used to heat the cemented carbide to improve its physical and mechanical properties. .
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