Grain refinement and anisotropy improvement of arc-directed energy deposited Ti–6Al–4V with oscillating laser

Abstract

Ti–6Al–4V parts fabricated by wire plus arc additive manufacturing (WAAM) usually exhibit columnar grain shapes and serious anisotropy in mechanical properties. This study aims to solve these issues by proposing a laser-assisted WAAM technique in which a vertically oscillating laser beam acts on the molten pool in WAAM. The influences of oscillation laser power on the microstructure and mechanical properties of Ti–6Al–4V parts built in WAAM are revealed and discussed. The oscillation laser can refine prior-β grains in WAAM. As the laser power increases, the depths of laser fusion lines in deposited layers increase, the size of prior-β grains decreases first and then increases, and both the microhardness and ultimate tensile strength (UTS) increase first and then decrease. At a laser power of 1600 W, the columnar prior-β grains are completely transformed into equiaxed shapes. The UTS values in the vertical and horizontal directions reach 1322 and 1309 MPa, respectively, respectively 30.5% and 15.7% higher than those of the WAAM sample. Meanwhile, the indices of plane anisotropy of UTS and elongation decrease by 90.6% and 76.4%, respectively.