The influence of ageing on the stability of β-γ/γ′ derived microstructures in Ni-Al-Cr-(Co) alloys

Abstract

Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with β(B2)-γ (A1)/γ′(L1₂), β-γ or β-γ′ microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of α-Cr, which can supplant the γ-phase during ageing of three-phase β-γ/γ′ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from β-γ/γ′ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L1₀ type martensite and interdendritic γ/γ′. Extensive intra- and interdendritic α-Cr precipitation was also observed. The stability during ageing of the interdendritic γ/γ′ microstructure is also considered and transformation of the L1₀ martensite is examined.