Microstructural evolution during powder metallurgical processing of a Ni3Si-based intermetallic alloy

The microstructural evolution of intermetallic nickel silicide powder was studied in the frame of the production of this material by hot isostatic pressing (HIP). The alloy contains some disordered phase to increase the toughness. The powder contains two nonequilibrium compounds—namely, Ni31Si12 and the metastable Ni74Si26 phase. Upon heating, these phases are eliminated, and the Ni3Si phase is formed. This decomposes above 920 °C, with the formation of Ni31Si12 and the disordered phase. This decomposition is contradictory to the binary phase diagram. It is concluded that additions of Cr and B destablize the L12 structure and promote the formation of Ni31Si12. To obtain a good strength of the material after HIP, a high HIP temperature is required. To meet the conflicting requirements of avoiding the Ni31Si12 phase and good cohesion of the material, thermal treatment after HIP is required to obtain a high strength and adequate ductility.