The influence of ageing on the stability of beta-gamma/gamma' derived microstructures in Ni-Al-Cr-(Co) alloys

Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with beta(B2)-gamma (A1)/gamma'(L1(2)), beta-gamma or beta-gamma' 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 alpha-Cr, which can supplant the gamma-phase during ageing of three-phase beta-gamma/gamma' microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from beta-gamma/gamma' is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L1(0) type martensite and interdendritic gamma/gamma'. Extensive intra- and interdendritic alpha-Cr precipitation was also observed. The stability during ageing of the interdendritic gamma/gamma' microstructure is also considered and transformation of the L1(0) martensite is examined.