Microstructural evolution of dual multi-phase intermetallic alloys composed of geometrically close packed Ni 3X (X: Al and V) type structures

Abstract

The microstructural evolution of intermetallic alloys, which have dual two-phase microstructure composed of Ni 3Al (L1 2) and Ni 3V (D0 22) 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 L1 2 phase and three D0 22 variant structures. With proceeding aging time, the decomposed L1 2 and D0 22 phases coarsened and transformed to lamellar-like microstructures where two types of interfaces between the L1 2 and D0 22 phases, and between two different D0 22 variant structures were developed. At longer aging time, the L1 2 phase disappeared from the lamellar-like microstructure and alternatively the D0 22 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 D0 22 variant structures tend to expend other set of two different D0 22 variant structures.