An Analysis of Notch Toughness of Electron Beam Powder Bed Fused (EB-PBF) Ti-6Al-4V in Relation to Build Orientation and Mechanical Properties

A comprehensive analysis of the notch toughness of Electron Beam Powder Bed Fused (EB-PBF) Ti-6Al-4V was conducted, which focused on the influence of build orientation and correlations with key mechanical properties. Horizontal and vertical specimens were fabricated with optimized process parameters and reused powder. The microhardness and microstructure of the metal were examined and both profilometry and scanning electron microscopy were used in evaluating the fracture surfaces. Results showed that the metal with vertical build orientation absorbed ~46% higher impact energy than the horizontal orientation due to crack propagation perpendicular to the prior-β grains, lower microhardness, and greater ductility. The importance of ductility to the vertical specimens was evidenced by greater shear lip width (~51%) and height (~35%), greater shear lip length (~18%), and higher roughness of the fracture surface (~15%). Shear width measurements showed the highest correlation with absorbed impact energy. Overall, results show that the notch toughness of EB-PBF Ti-6Al-4V is dependent on the build orientation due to differences in microstructure and the bulk mechanical properties. The notch toughness is well correlated with tensile properties as well. Lastly, a framework for relating the notch toughness in dynamic loading and quasi-static fracture toughness for EB-PBF Ti-6Al-4V is proposed.