MICROSTRUCTURAL EVOLUTION DURING POWDER METALLURGICAL PROCESSING OF ANI3SI-BASED INTERMETALLIC ALLOY

The microstructural evolution of intermetallic nickel silicide powder was studied in the frame of the production of this material by hot iso static pressing (HIP). The alloy contains some disordered phase to inc rease the toughness. The powder contains two nonequilibrium compounds- namely, Ni31Si12 and the metastable Ni74Si26 phase. Upon heating, thes e phases are eliminated, and the Ni3Si phase is formed. This decompose s above 920 degrees C, with the formation of Ni31Si12 and the disorder ed phase. This decomposition is contradictory to the binary phase diag ram. It is concluded that additions of Cr and B destablize the L1(2) s tructure and promote the formation of Ni31Si12. To obtain a good stren gth of the material after HIP, a high HIP temperature is required. To meet the conflicting requirements of avoiding the Ni31Si12 phase and g ood cohesion of the material, thermal treatment after HIP is required to obtain a high strength and adequate ductility. (C) Elsevier Science Inc., 1997.