Evaluation of the Mechanical property heterogeneity in laser-directed energy deposited Ti-6Al-4V alloy

Laser-directed energy deposition (L-DED) has emerged as a promising technique for prototyping and the rapid manufacturing of Ti-6Al-4V alloy components. However, the hierarchical and heterogeneous microstructure that forms during L-DED can potentially lead to localized mechanical property variations. As a result, the widespread application of L-DED Ti-6Al-4V depends on a thorough understanding of its local property heterogeneity. This study examines the mechanical properties of L-DED-fabricated Ti-6Al-4V alloy, with a particular focus on hardness and localized tensile properties within the build volume, to identify potential variations. The mechanical property heterogeneity of the alloy was assessed both in the as-deposited condition and after mill-annealing (MA) treatment. Interestingly, the hardness distribution in L-DED Ti-6Al-4V, whether in the as-deposited or MA condition, did not exhibit significant local variability. Local tensile strength variation was found to be influenced by the orientation of the columnar beta grains. When these grains were oriented perpendicular to the tensile deformation direction, minimal heterogeneity in tensile strength was observed. In contrast, greater variation was perceived when the columnar beta grains were aligned parallel (along the deposition direction) to the tensile deformation direction. Furthermore, the strain-to-failure was higher along the deposition direction than in the perpendicular orientation. Notably, the strain-to-failure of the L-DED Ti-6Al-4V alloy decreased following MA treatment, regardless of the grain orientations. No clear trend in strain-to-failure variation with sample location was observed in L-DED Ti-6Al-4V alloy, either in the as-deposited or MA conditions. The observed local heterogeneity in mechanical properties is discussed and explained based on microstructural features and their influence on deformation behavior in the L-DED Ti-6Al-4V alloy.