Effect of α texture on the anisotropy of yield strength in Ti–6Al–2Zr–1Mo–1V alloy fabricated by laser directed energy deposition technique

Abstract

Near α titanium alloys fabricated by laser directed energy deposition (LDED) technique always display strong anisotropies of mechanical properties even they only contain a small amount of strong-textured β phase. This work gives a detailed investigation on the effect of α texture on the anisotropy of yield strength of a laser directed energy deposited (LDEDed) Ti–6Al–2Zr–1Mo–1V (TA15) alloy by consideration of the solid phase transformation. Results indicate that the yield strength of LDEDed TA15 alloy along three directions, the building direction (VD), the horizontal direction (HD) and 45° direction (OD), shows dramatically differences of 899.7 MPa, 937.3 MPa and 1016.7 MPa. The α texture is transformed from strong β texture respected to Burgers orientation relationship with weak variant selection. The crystallographic orientation and spatial orientation of textured α phase are the key factors to dominate the yield strength of LDEDed TA15 alloy at different loading directions. Along the VD direction, strong intensity of texture is found in the easily-activated <101¯1> and <112¯0> orientation of α phase, resulting in the largest Schmid factor. However, strong intensity along the OD direction in the hardly-activated <0001> orientation for basal and prismatic slip system of α phase leads to the lowest Schmid factor. The spatial orientation of textured α phase also affects the effective slip distance, which leads to the difference of resolved shear stress in different loading directions. The coupled effect of Schimd factor and effective slip distance controlled by transformed α texture mainly results in the anisotropy of yield strength.