Effect of Build Orientation on Metallurgical and Mechanical Properties of Additively Manufactured Ti-6Al-4V Alloy

The additive manufacturing of Ti-6Al-4V alloy components has become popular in the fields of aerospace and biomedical devices. One of the most difficult aspects of additive manufacturing is fabrication of components with reproducible metallurgical and mechanical properties in different build orientations. This article presents a comprehensive study on the effect of build orientation in laser-powder bed fusion (L-PBF) technique of additive manufacturing. The additively manufactured samples were also heat treated to relieve the residual stress. In the as-built condition, the 0° build-oriented flat sample (with build direction along thickness) exhibited high tensile strength of 1202 MPa as well as high microhardness of 481 HV, but low ductility. The upright (90° build-oriented) samples had the largest elongation of 8% but low density (4.336 g/cm3) and high tensile residual stress of 163 MPa. Inclined (45° build orientation) sample provides the least tensile residual stress in as-built condition but not after the heat treatment. Defects like pores, un-melted or partially melted powder particles, and cracks contribute to the low tensile strength and high surface roughness in various build orientations. The associated residual stresses are reduced by heat treatment but at the expense of some loss in strength. The fracture mechanism is dependent on the growth direction of the microstructure. This study points out toward the necessity of considering build orientation as an important decision variable in the process optimization.