Vacuum sintering of powder metallurgy
The main advantages of vacuum sintering are:
(1) reduce the adverse effects of harmful components (water, oxygen and nitrogen) in the atmosphere of the products. For example, the water content drops to electrolytic hydrogen 4. Dew point is difficult, as long as the vacuum reaches 133pa 4 equivalent moisture content. Dew point temperature. It is not difficult to obtain such a vacuum.
(2) vacuum sintering materials can be used to carburize materials that are not used in reduction or inert gases as protective atmosphere (such as sintering of active metals) or easy to decarbonize.
(3) vacuum can improve the wettability of solid relative to liquid, improve the alloy, and facilitate the contraction of the structure.
(4) it is helpful for vacuum sintering impurities such as silicon, aluminum, magnesium or calcium oxide to purify the material.
(5) vacuum gas adsorption is conducive to removal, while residual gas plays an important role in promoting shrinkage after sintering in the pores of reaction gas products. For example, the vacuum degree of porous sintered cemented carbide is obviously lower than that of hydrogen sintered cemented carbide.
(6) the protective vacuum sintering temperature is lower than the sintering temperature of the gas, for example, the sintering temperature of hard alloy can be reduced by 10. 150 ℃. This is conducive to reducing energy consumption and preventing food growth. In vacuum sintering, volatile metal loss often occurs. If the carbide bit volatilizes. By strictly controlling the vacuum degree, even if the furnace pressure is no lower than the vapor pressure of sintered metal components, the loss of volatile metals can be greatly reduced or avoided. Another problem is the vacuum decarburization and sintering of carbonaceous materials. This occurs mainly during the heating phase, where residual gases in the furnace, oxygen, water, and other reactive oxide powders may react with carbon-free carbides in the carbon material or with carbon monoxide in the furnace gas. Decarburized carbon materials can improve the carbon content of powder and control the vacuum degree. In order to improve the heating speed and temperature uniformity of the vacuum sintering furnace, the initial amount of sintering gas (inert gas or hydrogen) can be introduced. The same gas cooling loop suppression method can be recycled to improve the cooling rate of vacuum sintering. In order to prevent contamination of sintering vacuum forming agent system, vacuum sintering should be carried out first, and then the forming agent should be excluded.
In powder metallurgy, vacuum sintering is mainly used for sintering of active and refractory metals, society, chin, error, TAM, saw, etc. Sintered hard alloy, magnetic alloy, tool steel and stainless steel; And sintering reaction of compounds prone to hydrogen, nitrogen, carbon monoxide and other gases.