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

The quenched in state of short range order in Ni70Mo25Al5 alloy was found to be characterized by intensity maxima at {100} 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 alloves. Transmission electron microscopy studies of the decomposition ofthe short range ordered alloy, into two long range ordered phases having the DO22 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 sigma-phase, found in both the Lis solutionised and the aged alloys. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.