Dual multi-phase intermetallic alloys composed of geometrically close-packed Ni3X (X: Al, Ti and V) type structures – I. Microstructures and their stability

The constitution and microstructure of intermetallic alloys based on the Ni3Al–Ni3Ti–Ni3V pseudo-ternary system and composed of the phases L12, DO22 and DO24 were investigated. Particular emphasis is paid to alloys with a relatively low Ti content. High-temperature annealing of these alloys leads to the formation of a two-phase microstructure at the micron-scale, which consists of the phases L12 + A1. This microstructure can additionally be refined by a decomposition reaction occurring upon annealing below the eutectoid temperature, according to which the Al phase is transformed into the L12 + DO22 phases. In this way, a novel microstructure is formed at the sub-micron scale. The dual multi-phase intermetallic alloys exhibit highly coherent interface structures between the constituent phases of L12 and D022 not only at a micron scale but also at a sub-micron scale and also display high microstructural stability at high temperature.