TEM observation of the channel regions in a two-phase intermetallic alloy based on Ni3Al–Ni3V pseudo-binary alloy system

A new type of intermetallic alloy with a two-phase microstructure composed of Ni3Al (L12) and Ni3V (D022) phases was investigated by using a transmission electron microscope (TEM), focusing on the microstructures in the channel regions. TEM bright-field images indicated that the two-phase microstructure consisted of well-defined primary Ni3Al precipitates and channel regions with peculiar contrast. In the narrower channel regions, single Ni3V variant structures, whose c-axis is normal to {1 0 0} plane of the primary Ni3Al precipitates, were observed. In the wider channel regions, the lamellar-like microstructures that are composed of alternately arranged two-types of Ni3V variant structures whose c-axes are perpendicular to each other were observed. The lattice misfit between the a-axis of Ni3Al and the c-axis of Ni3V was determined to be larger than that between the a-axis of Ni3Al and the a-axis of Ni3V. It was suggested that the crystallographic orientation of the Ni3V phase in the channel regions was aligned in the manner of lowering an internal stress due to the lattice misfit between the primary Ni3Al precipitates and the Ni3V domains.