Koji Hayashi1 and Hiroshi Kihara1
1Institute of Industrial Science, The University of Tokyo, Tokyo
The green compact from Fe ultrafide powder (average particle size, 0.02 μ m; oxygen content, 15 mass%) was pressure-sintered under 100 and 200 MPa at 673~973 K for 1.8 ks in flowing hydrogen, after the reduction of the iron oxide. The densification temperature, crystal grain size and hardness of the compact were investigated, in comparison with those in the case of pressureless-sintering.
The results obtained were as follows; (1) The nearly full densification temperature under 100 and 200 MPa were lower by about 150 K and above 300 K respectively than that (970 K) in the pressureless-sintering. (2) The minimum value of the average grain size in the dense pressure-sintered compact was about 0.15 μ m, which was much smaller than 1.2 μ m of the pressureless-sintered compact. (3) The hardness of the pressure-sintered compact with the grain size of 0.15 μ m was as high as about 385 HV, compared with about 85 HV of the usual coarse-grained iron metal. The Hall-Petch linear relationship between HV and the square root of the grain size was confirmed to hold also for the grain size range larger than about 0.15 μ m.
iron powder, ultrafine metal powder, pressure-sintering, ultrafine grained iron, densification, grain growth, hardness
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