Microstructural evolution of dual multi-phase intermetallic alloys composed of geometrically close packed Ni3X (X: Al and V) type structures

The microstructural evolution of intermetallic alloys, which have dual two-phase microstructure composed of Ni3Al (L12) and Ni3V (D022) phases, was investigated as a function of aging time at 1273 K, using transmission electron microscopy and X-ray diffraction. Even from early aging time, the lower (i.e. eutectoid) microstructure showed structurally decomposed clusters composed of L12 phase and three D022 variant structures. With proceeding aging time, the decomposed L12 and D022 phases coarsened and transformed to lamellar-like microstructures where two types of interfaces between the L12 and D022 phases, and between two different D022 variant structures were developed. At longer aging time, the L12 phase disappeared from the lamellar-like microstructure and alternatively the D022 phase composed of two different variant structures prevailed over the lamellar-like microstructures. Corresponding to this microstructural change, the direction of the lamellar and its interfacial plane rotate (i.e. change) from 〈001〉 to 〈011〉 and from {001} to {011}, respectively. At a final aging stage, a specific set of two different D022 variant structures tend to expend other set of two different D022 variant structures.