TEM observation of the channel regions in a two-phase intermetallic alloy based on Ni 3Al–Ni 3V pseudo-binary alloy system

Abstract

A new type of intermetallic alloy with a two-phase microstructure composed of Ni 3Al (L1 2) and Ni 3V (D0 22) 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 Ni 3Al precipitates and channel regions with peculiar contrast. In the narrower channel regions, single Ni 3V variant structures, whose c-axis is normal to {1 0 0} plane of the primary Ni 3Al precipitates, were observed. In the wider channel regions, the lamellar-like microstructures that are composed of alternately arranged two-types of Ni 3V variant structures whose c-axes are perpendicular to each other were observed. The lattice misfit between the a-axis of Ni 3Al and the c-axis of Ni 3V was determined to be larger than that between the a-axis of Ni 3Al and the a-axis of Ni 3V. It was suggested that the crystallographic orientation of the Ni 3V phase in the channel regions was aligned in the manner of lowering an internal stress due to the lattice misfit between the primary Ni 3Al precipitates and the Ni 3V domains.