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

Abstract

A layered α/β Ti alloy was developed by cold rolling and subsequent aging heat treatment of a metastable β Ti-12Mo alloy. The microstructure consisted of coarse equiaxed β grains containing a large number of deformation twins. After aging, α 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 α 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 α” martensite inside thick twins and ω 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 α layer at the interface between the matrix and thick twins. This heterogeneity was finally discussed based on an elastic stiffness analysis and the specific crystallographic configuration at this interface.