Microstructural evolution and mechanical properties of new multi-phase NiAl-based alloy during heat treatments

Microstructural evolution and the relationship between microstructure and property during heat treatments in a new NiAl-based alloy (Ni-26.6Al-13.4Cr-8.1Co-4.3Ti-1.3W-0.9Mo, molar fraction, %)) were investigated. The as-cast alloy is composed of NiAl matrix and Cr3Ni2 phase with poor ductility. The Cr3Ni2 phase is distributed as a network along the NiAl grain boundaries. Subsequent heat treatment (1 523 K, 20 h, air cooling+1 123 K, 16 h, furnace cooling) leads to the dissolution of Cr3Ni2 phase and the precipitation of lath-shaped Ni3Al phase and α-Cr particles, resulting in the improvement of compressive properties and fracture toughness at room temperature. Followed by long-term thermal exposure (1 173 K, 8 500 h), it is found that the residual Cr3Ni2 phase keeps stable while the α-Cr particles coarsen and a great mass of lath-shaped Ni3Al precipitates are degenerated, which compromises most of the above improvements of mechanical properties through heat treatment.