Development of High Strength and Superplasticity in the Heat-refined (NiAl+Ni3Al) Two-Phase Alloy

Effect of heat treatment on the microstructures and mechanical properties of (NiAl+Ni3Al) two-phase alloys was investigated. A martensitic transformation was observed when the Ni-Al alloys were quenched from 1573 K. The martensite resulted in a fine two-phase structure consisting of NiAl and Ni3Al by tempering at 1073 K. Very fine lamellar structures having an equal volume fraction of the two aluminides were obtained at 34.0 mol%Al. The two-phase alloy showed high compressive strength at low temperatures. On the other hand, the flow stress of the alloy was lower than that of each constituent phase and showed an almost constant value during the plastic deformation at high temperatures such as 1073 K. The strain rate sensitivity exponent of the alloy was found to be about 0.4, which suggests that the superplastic flow occurred in the high temperature deformation of this fine two-phase alloy.