Microstructure and texture development in Ti-15V-3Cr-3Sn-3Al alloy – Possible role of strain path

Abstract

In the present investigation, evolution of microstructure and texture was studied for a β titanium alloy during cold rolling (unidirectional rolling (UDR) and cross rolling (multi-step cross rolling (MSCR) and two step cross rolling). For both UDR and MSCR of initially hot rolled alloy consisting of elongated and equiaxed grain structure, the occurrence of shear bands inside the grains was the main feature of the microstructure. The density of these shear bands was dependent on the cold rolling reduction and strain path and was found to be orientation dependent. Shear bands preferentially occurred in γ-fiber (normal direction (ND)//〈111〉) oriented grains. The regions with shear bands had higher hardness than the regions without shear bands, and {111}〈112〉 component of the γ-fiber was found to be more susceptible to formation of shear bands. The orientation dependence of these shear bands was analyzed within the framework of Dillamore's plastic instability criterion. During UDR, strong α and γ-fibers were observed after highest strain (ε = 1.6), while strong rotated cube ({100}〈110〉) texture developed after MSCR at highest strain (ε = 1.6). The volume fraction of both α and γ fibers gradually increased with the increase in cold rolling reduction during UDR. For MSCR, the rotated cube component gradually increased with increase in cold rolling reduction. In solution annealed β-Ti alloy with equiaxed grain structure, α and γ fibers were formed after highest strain (ε = 1.6) during UDR. However, due to large grain size, both α and γ fibers were discontinuous. The texture development was found to be more strongly dependent on the strain path than the initial microstructure during cold rolling.