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.

Static and in-situ high-resolution transmission electron microscopy investigations of the atomic structure and dynamics of massive transformation interfaces in a Ti-Al alloy

“…apart) are shown in Figure 11(b), viewed along the z-axis over an expanded area of interface, which was 13 ϫ 13 nm. It is apparent from Figure 11(b) that the NCSs in the high-index IPs, [38] further indicating that the interface is also plotted as small dots. This figure reveals the somewhat corrugated nature of the interface in relation to the NCSs.…”

“…It is important to of the structure and motion, the observation of stepwise motion at the interface is definitive, even on an inclined note that the interface advanced one moire spacing at a time, indicating that the height of the steps on the interface (0. 38 interface. It is important to note that the OR between the ␣ 2 and ␥ M phases is constant in Figures 14 and 16, so that nm in projection) is constant and dictated by good planar matching.…”

Crystalline characteristics of alpha precipitates in Ti–15V–3Sn–3Al–3Cr alloy

“…in Ti-22V-4Al and Ti-15V-3Cr-3Sn-3Al alloys. It was reported by Miyano et al (2002b) that an intra-granular precipitate with Burgers O.R. had a lower free energy of formation for the critical nucleus than one with the Potter O.R.…”

Comparison of interfacial structure-related mechanisms in diffusional and martensitic transformations

“…Such boundaries can be glissile when they contain transformation dislocations lying at an angle with respect confirmed the separate existence of MCD by means of a near O-lattice model, [57,66] the near coincidence site to the apparent habit plane and meeting a slip plane in the matrix, edge-to-edge at a small angle. These dislocations model [65][66][67][68] and direct inspection of the dichromatic complex of the crystal structures forming the MCD, [69] all of which led are disconnections [40,41] with a Burgers vector significantly smaller than that of a lattice dislocation. When dislocations independently to the same result.…”