Electron microscopic determination of orientation

Abstract

The martensites of titanium binary alloys, containing 1, 2, and 5.3 wt pct Cu, were studied by transmission electron microscopy techniques. Roughly parallel plates with different variants of the orientation relationship, as well as colonies of identical variant plates, prevail in the structures. A stereographic projection analysis of super-imposed diffraction patterns from two adjacent plates is shown to be sufficient for the deduction of the orientation relationship that existed during transformation, which is found to be the Burgers’ relationship -(110)_β∥ (0001)_α′; 〈111〉_β∥ 〈2110〉_α′. A graphical method was developed for the derivation of the habit plane and its particular variant, in spite of the absence of retained β phase in quenched Ti-Cu alloys. The habit plane of Ti-Cu martensite is found to be (1079)_β with 4 deg accuracy, and to best agree with Class A (α^- ω⁺) solution of the Bowles and Mackenzie theory, rather than with (α⁺ ω⁺) or with Class B solutions.