Koji Hayashi1 and Hiroshi Kihara1
1Institute of Industrial Science, The University of Tokyo, Tokyo
The densification of compacts from Fe and Cu ultrafine powders (average particle sizes, 0.02 and 0.05 μ m, respectively; oxygen contents, 15 and 6 mass%, respectively) and the average grain size in the sintered compact were investigated in relation to the relative density (Dg) of the green compact, heating-rate (dT/dt) and sintering temperature.
The sintered compact with full density and almost free from oxygen or oxide was obtained by sintering at 973--1073 K for each powder, when the sufficient reduction and also degasification were made to take place by decreasing both Dg and dT/dt to values considerably smaller than those usually set for normal coarse powders. In the case of large Dg and/or dT/dt, the Fe and Fe-50%Cu sintered compacts contained a large amount of remaining oxygen or oxides, although they were fully dense; the Cu compact was not fully dense, although it was free from oxygen. The reason for the difference was able to be explained from the viewpoint of PH_2O/PH_2 equilibrium pressure ratio in the reduction of the oxide by hydrogen. The average grain sizes in the fully dense and oxygen free sintered compacts were as small as 0.3--1.5 μ m, although they were considerably larger than those of starting powders.
ultrafine powder, iron, copper, sintering, densification, grain growth, fine microstructure
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