Effect of Aging Treatment on R Transformation in Nanocrystalline Ti–50.9 at.% Ni Alloy

Effects of the size, morphology, and spatial distribution of coherent Ti3Ni4 particles in a nanocrystalline Ti– 50.9 at.% Ni alloy with an inhomogeneous grain-subgrain structure on the B2 → R transformation and the morphology of the R phase are studied. It has been found that the morphology of the R phase in the alloy depends on the aging temperature and changes from nanodomain observed after low-temperature aging (300°C) to lamellar self-accommodative morphology formed under conditions of intense particle precipitation (400°C). It is shown that this is due to a change in the spatial distribution of particles from location on dislocations to precipitation near low-angle boundaries. In the case of lamellar morphology of self-accommodation, the R-plates reorientation develops localized in a Lüders-like manner.