HRTEM Observation and Atomic Modeling of α/β Interphase Boundary in a Ti-22V-4Al Alloy

Abstract

In order to study interface boundary structures, a three dimensional Near-Coincidence Site lattice (Near-CSL) model based on Bollmann’s O-lattice method has been proposed. Previous studies have shown that intragranular α-phase precipitates in a Ti–22V–4Al alloy have a morphology of lath-like, with two well defined facet planes. A detailed TEM observation of the laths has been made in this study and the results correlated to the present analysis. Accommodation mechanism of misfit dislocations and the Burgers vector of the defects observed at the broad face and side facet plane of the intragranular α-phase precipitates have been determined. The structural ledges at the side facet, as predicted by the present analysis, is consistent with HRTEM observation. The Burgers vector of misfit dislocations at the broad face is in good agreement with that previously reported for a Zr–2.6Nb alloy, that has almost the same lattice parameter ratio as the Ti–22V–4Al alloy used in the present study. Although the Burgers vector of the defects on the broad face can be determined by HRTEM observation, the boundary plane is not well defined. However, it can be demonstrated that the interface boundary structure of the broad face can be rationalized from the results of both the Near-CSL analysis and the HRTEM observations.