Crystallography and deformation behavior of α phase precipitate at twin/matrix interface in a cold rolled metastable Ti-12Mo alloy

A layered alpha/beta Ti alloy was developed by cold rolling and subsequent aging heat treatment of a metastable beta Ti-12Mo alloy. The microstructure consisted of coarse equiaxed beta grains containing a large number of deformation twins. After aging, alpha phase was found to preferentially precipitate at twin boundaries following a fixed crystallographic orientation relationship with respect to both the twin and the matrix. Finely dispersed alpha precipitate were also observed in the matrix and inside some thick twins and were inferred to be due to the presence of parallel nano-sized alpha" martensite inside thick twins and omega phase formed during cold rolling. The deformation behavior of aged sample was finally characterized by a combination of digital image correlation (DIC) and electron backscatter diffraction (EBSD) analyses. An increase in yield strength was noted when compared with the solution treated sample. It was found that plastic deformation was highly heterogeneous and mostly located in the alpha layer at the interface between the matrix and thick twins. This heterogeneity was finally discussed based on an elastic stiffness analysis and the specific crystal-lographic configuration at this interface. (C) 2021 Elsevier B.V. All rights reserved.