The influence of alloying on the microstructure and mechanical properties of P/M Ni3Al

The influence of alloying additions of iron and chromium alone and in combination with molybdenum and zirconium on the heat treatment response and mechanical properties of powder metallurgy processed Ni₃Al based materials have been characterized. Additions of 8 at.% Cr result in considerable solid solution strengthening, while 11 at.% Fe by itself has little effect on the yield strength. Additions of both iron and chromium result in an alloy with higher strength than either unalloyed Ni₃Al or alloys with either element alone, however, the ductility is reduced by formation of β′ phase. The alloys containing Fe or Cr alone and the unalloyed material are essentially single phase γ′ after heat treating at 1000°C for 1 h, while the more complex alloys have a significant volume fraction of disordered γ phase. The alloys with a high degree of order exhibit large yield drops and corresponding Lüders strains. As the amount of disorder increases the magnitude of both the yield drop and Lüders strain decreases. Values of the power law hardening exponent for the alloys are found to be as high as 0.8 and generally decrease as the amount of γ phase increases as a result of alloying. All of the materials have high strain rate sensitivity at elevated temperature combined with resistance to grain growth that suggests they will deform superplastically.