Aging effect on microstructure and hardness of two-phase Ni3Al–Ni3V intermetallic alloys containing Ta and Re

Two-phase intermetallic alloys composed of geometrically closed packed (GCP) Ni3Al (L12 phase) and Ni3V (D022 phase) have very attractive mechanical properties at high temperatures and are therefore being considered for use as high temperature structural materials. In this study, it was found that the addition of Ta remarkably enhanced the alloys’ hardness due to solid solution hardening in the constituent phases but did not result in an age hardening effect. On the other hand, the addition of Re inhibited the formation of the two-phase microstructure in the solution treated condition, resulting in the lowest hardness. After aging at 1223 K, the Ni solid solution phase in the channel region of the Re-added alloy was decomposed into Ni3Al and Ni3V, accompanied by the precipitation of a Re-rich phase. Consequently, the hardness rapidly increased with increasing aging time. Simultaneous addition of Ta and Re induced fine, dense precipitation of Re-rich phase after aging and consequently resulted in higher hardness than the addition of Ta or Re individually.