Abstract
The green compacts of Fe+(25-80)%Co and Fe+(25-75)%Ni mixed ultrafine metal powders (average particle size of Fe, Co and Ni each powder, 0.02 μm) were mainly pressure-sintered under 100-500 MPa for 3.6 ks in H2 gas, after the reduction of the oxide. The lowest temperature for complete densification (Tsc), the average crystal grain size and hardness (HV) of the sintered compacts were investigated, compared with the results on Fe, Co and Ni single component powders.
The results obtained were as follows: (1) The Tsc under 500 MPa for Fe+50 at%Co and Fe+50 at%Ni mixed powder compacts were about 700 and 680 K respectively, which were higher by 100-210 K than those for single component powder compacts. (2) The minimum of the average crystal grain size of the nearly dense compacts, which were sintered at 640 K under 500 MPa, were about 0.12 μm at 50 at%Co and 0.11 μm at 25 at%Ni respectively. These were smaller by about 0.03-0.14 μm than those of single component compacts obtained under the same condition. (3) The highest hardness of the Fe-Co and Fe-Ni sintered compacts were about 870 HV at 50 at%Co and 730 HV at 25 at%Ni, which were higher by 100-200 HV than those of single component compacts at the same crystal grain size and higher by about 600-700 HV than those of usual coarse-grained metals. The Hall-Petch linear relationship was observed to hold for the hardness of Fe-50 at%Co and Fe-50 at%Ni single phase compacts.
