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TZM alloy Deoxidation Mechanism Analysis during Vacuum Sintering

The experiment found that TZM alloy during powder metallurgy sintering process mainly has two kinds of deoxidation mechanisms: the first one, metal oxide of carbon reduction system to form metal carbides and CO; the second one, MoO₂ happening disproportionation reaction at vacuum high temperature to form metal Mo and MoO₃ gas, where the MoO₃ gas will be discharged by vacuum system.

Firstly, analysis the influence of carbon content on TZM alloy deoxidation during vacuum sintering. Experiment arrangement as follows: adding 0.5% TiH_x and 0.09% ZrH_x into molybdenum powder, and then dividing the sample into three parts, in the sample were added 0.04%, 0.07%, 0.10% different proportions of carbon, and finally made TZM alloy rods. Tested oxygen content and the carbon content of TZM alloy bar found C element content and TZM alloy deoxidation effect is proportional to, but excess carbon can cause alloy component failure.

In addition, the oxygenium of molybdenum mixed powder mainly decisions by oxygen content of molybdenum powder. Molybdenum powder after the reduction reaction, the mainly existing way of oxygen is molybdenum oxide, which the most stable is MoO₃ and MoO₂, and MoO₃ in a vacuum and high temperature will volatilize into a gas, so at high temperature molybdenum oxide mainly exists by MoO2 form. The experiment found that in the case of high temperatures and the absence of air, MoO₂ happen disproportionation reaction to produce metal Mo and gaseous MoO₃, and gaseous MoO₃ will be discharged by vacuum system.

TZM alloy deoxygenation process mainly achieved by carbon reaction and disproportionation reaction of MoO₂ which occurs in high-temperature vacuum sintering process. The reaction temperature and air pressure of product in vacuum furnace will have great impact on the quality of these two reactions. Reducing the partial pressure of product and improving vacuum degree can reduce the deoxygenation reaction temperature of the beginning which is good for reducing oxygen content of TZM alloy.

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