Abstract
The authors had been interested in the sintered densities of MIM(metal injection molding) products : The sintering densification of the products were incomplete. The sintering densification of Cu, Cu-Sn, Cu-Ni and carbonyl iron fine powders for MIM were investigated under various conditions. It was found that the densification of Cu, Cu-Sn and Cu-Ni powders levelled off at about 95% of the theoretical density when sintered in H2 gas, but became complete when sintered in vacuum or by thee addition of foreign element which forms stable oxide or has low standard free energy(ΔGf°) of oxide formation. The carbonyl iron powder also showed incomplete densification when sintered in vacuum as well as H2 gas, but showed complete densification when the elements of low ΔGf° were added. These phenomena could be explained in general from the present authors' theory of gas pressure, i.e., whether the equilibrium pressure of gas generated in the reduction reaction of the oxide is larger or smaller than the surface stress(the driving force of shrinkage) of closed pores is one of the determining factors for the incomplete or complete densification.
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