Development of Microstructure and Crystallographic Texture during Stationary Shoulder Friction Stir Welding of Ti-6Al-4V

Abstract

Electron backscattering diffraction (EBSD) was used to study a stationary shoulder friction stir weld in Ti-6Al-4V. Weld temperatures exceeded the β-transus, resulting in a supertransus zone (STZ) that encompassed all of the thermomechanically affected zone (TMAZ) and a portion of the heat-affected zone (HAZ). Standard EBSD provided limited information on the material behavior at high temperature in the β phase field, so in-house software was used to reconstruct the crystallographic orientations of the high-temperature β phase. The portion of the HAZ that lay within the STZ exhibited the same β texture at high temperature as the retained β phase in the unaffected parent material. In the TMAZ, material was deformed in the high-temperature β phase field and, on cooling, transformed to a fully lamellar microstructure. The β textures at high temperature were dominated by the D 2 $$ \left( {\bar{1}\bar{1}2} \right)\left[ {111} \right] $$ simple shear texture component. The α phase textures in the fully lamellar microstructure that formed on cooling were inherited from the shear textures of the β phase, but significant variant selection occurred.