Alloying effect on stability of multi-variant structure of Ni3V at elevated temperatures

A stoichiometric tetragonal compound of Ni3V (D022) quenched from disordered fcc (A1) state exhibits a unique morphology of ‘multi-variant structure’ (MVS) where the three variants of D022 are periodically arrayed with coherent {102)D022 and {010)D022 interfaces. The MVS of this compound collapses rapidly accompanied with coherency loss at the variant interfaces during aging at elevated temperatures. The collapse is caused by the rigidity of the variants filling in the {102)D022 and {010)D022 channels between the major variant particles. Introduction of disordered fcc (A1) phase to the channels by alloying addition makes the MVS stable without coherency loss of the interfaces even after prolonged aging. The resulting two-phase microstructure, so called maze and chessboard microstructure, exhibits a different shape of D022 variant with various habit planes, depending on the lattice misfit strains along a- and c-axes of D022, δa(<0) and δc(>0), respectively. The factor to determine the shape of variant is δa, whereas that to determine habit plane is the misfit ratio, δc/δa, The morphology map is constructed as functions of δa and δc, and the shape of the D022 variant changes from plate to prism as the value of |δa| becomes smaller than 0.002, results in the chessboard microstructure.