Ordering and topologically close packed-phase precipitation in a Ni–25at.%Mo–5at.%Al alloy

Abstract The quenched in state of short range order in Ni70Mo25Al5 alloy was found to be characterized by intensity maxima at {1 0 0} and equivalent positions in the reciprocal space, in addition to the {1 1 2 0} and equivalent maxima seen in the case of the binary Ni–Mo alloys. Transmission electron microscopy studies of the decomposition of the short range ordered alloy, into two long range ordered phases having the D022 and the Pt2Mo-type structures, at ageing temperatures of 875 and 1000 K have been carried out, in addition to microstructural characterization of the topologically close packed phases, such as the σ-phase, found in both the as solutionised and the aged alloys.