Crystallographic rotation of Ti-6Al-4V alloy with a fiber texture component under isothermal forging through experimental and CPFEM analyses

Abstract

This study examined the crystallographic rotation behavior of α phase in a Ti-6Al-4V alloy under isothermal uniaxial forging at 800 ℃ and 850 ℃ with changing strain rates. The base material of a Ti-6Al-4V alloy bar comprised a strong <101¯0> fiber texture component along the longitudinal direction (designated as the Z-direction in this study). Compression tests (until a height reduction of 50%) were conducted along the Z-direction and radius direction, which is perpendicular to the Z-direction (hereafter designated as the Y-direction). Microstructural conversions for the forging conditions with strain rates lower than 10−1 s−1 occurred under continuous dynamic recrystallization in which grain sizes became finer under deformation. However, only at the high strain rate condition of 1 s−1, grain refinement accompanied by significant crystallographic rotations of [0001] from the radius direction to the longitudinal direction occurred when compressed parallel to the Z-direction. This study investigates the origin of the significant rotation of [0001] observed during compression along the Z-direction at a high strain rate of 1 s−1 through experimental and crystal plasticity finite element analyses. The results show that the anisotropic dislocation glides among prismatic <a>, basal <a>, and pyramidal <c+a> led to the significant rotation of [0001] under isothermal forging at a high strain rate of 1 s−1. Furthermore, the possibility of the frequent occurrence of twinning is discussed, and it was determined to be lower than that of the anisotropic dislocation glide for the origin of the significant rotation of [0001] observed during forging at a high strain rate of 1 s−1. Alternatively, a sub-grain formation and its rotation occurred at strain rates below 1 s−1, corresponding to the process condition of the enhanced thermally activated process.