Controllable mechanical anisotropy of selective laser melted Ti6Al4V: A new perspective into the effect of grain orientations and primary grain structure

Abstract This work investigated the significantly weakened anisotropy of tensile properties of selective laser melted Ti6Al4V by heat treatment and represented a new perspective into the weakening mechanism. For the as-deposited sample, the tensile strength showed an evident improvement as the oriented angle θ (the angle between the tensile axis and the substrate plane) increased from 0° to 90° while the elongation showed the opposite trend. Nevertheless, the heat treatment weakened the anisotropy of strength as the deviation was reduced from 167 to 39 MPa, while the anisotropy of ductility was also remarkably declined. An algorithm, based on the EBSD data, was newly adopted to determine the most likely active slip system of each grain and evaluate the area-weighted average Schmid factors (SFs). The statistical results presented the distinct difference in the SFs of the as-deposited sample as θ changed while the SFs of the heat-treated sample showed similar values, quantitatively explaining the anisotropy of strength and the weakening mechanism. Besides, the high dependence of SF on the primary β grains, the number of primary β grains in the tensile specimen at different θ, and the existence of equiaxed grain boundary α together explained that ductility was worst at θ = 90° and increased as θ decreased.