Liquid phase sintering of fe-cu super-saturated solid solution powders produced by mechanical alloying

Fe-Cu super-saturated solid solution powders were prepared by mechanical alloying of the elemental Fe and Cu powders, and the sintering behavior of the mechanically alloyed powders was investigated in association with the separation behavior of the liquid Cu phase. The chemical compositions of the mechanically alloyed powders were 10 similar to 33 mass%Cu. The powders obtained were very hard in the as-milled state, so that they were subjected to a softening treatment of 1173 K-0.6 ks, and then compacted to test pieces using metallic die. Sintering of the pow der compacts was performed at 1373 K which is just above the melting point of copper. During the ball-milling of Fe-Cu powder mixtures, an extremely large energy is stored within powder particles and single-phase bcc solid solutions are synthesized for the alloys of up to 25 mass%Cu. The large stored energy leads to grain-refining of the (alpha-Fe + epsilon-Cu) two-phase structure formed in subsequent softening treatment. In the early stage of sintering, the liquid Cu phase oozes onto the grain boundaries to separate fine gamma-Fe grains, and the rearrangement of separated gamma-Fe grains results in densification of Fe-Cu powder compacts, For example, an Fe-25 mass%Cu powder compact, in which the liquid Cu phase oozed homogeneously, was densified to 98% in relative density only by sintering treatment, without singnificant coarsening of the microstructure. The sintered material has fine alpha-Fe grains of less than 20 mu m even after sintering of 1373 K-3.6 ks.