Abstract
Wide range selected area electron diffraction (SAD) patterns on ⟨110⟩ crystal-zones (CZ) of a single variant of R-phase in Ti–50.4 at%Ni alloy quenched from 1223 K indicated that the ⟨110⟩ CZs can be classified into two types, CZ-A and CZ-B, with respect to the 1⁄3⟨110⟩∗ reflections. Especially the absence of 1⁄3⟨110⟩∗ on the CZ-A could not be explained by the models proposed up to now. Based on the experimental results, a map that expressed the SAD patterns of single R-phase variant on the (111) stereographic projection was presented. It was suggested that the true structure of R-phase should fulfill three conditions on characteristics of SAD patterns, that is, the reproduction of the unique (111) pattern, the absence of 1⁄3⟨110⟩∗ reflection at the specific planes on CZ-A and the retainment of three-fold symmetry with respect to the [111]. Bending the TEM sample composed of several R-phase variants caused the integration of the R-phase variants, and resulted in the formation of the B19′ martensite. However both the single variant and the B19′ martensite returned to the initial state of several R-phase variants after 120 hours at room temperature. It was proposed that the unification of the R-phase variants plays an important role on the R-M transformation.
