Build Orientation Effects on Microstructure and Damage Evolution of Selective Laser Melted in718 Alloy

This study reveals the synergistic mechanism of build direction and heat treatment on the microstructure, mechanical properties, and damage evolution behavior of selective laser melted (SLM) IN718 alloy. The results demonstrated that the mechanical properties of as-deposited alloys exhibited significant directional dependence: the 0°-oriented specimens showed higher tensile strength of 1001 MPa, while the 90°-oriented specimens exhibited superior plasticity with elongation of 19.9%. After heat treatment, microstructural segregation was eliminated, and δ phases precipitated at grain boundaries. The tensile strength of 0°-oriented specimens increased by 37.4%, surpassing the 26.4% enhancement observed in 90°-oriented specimens. Quantitative characterization of damage evolution behavior via nanoindentation technology indicates that the 90°-oriented specimens exhibit slower elastic modulus degradation in the early stage of damage, with a higher critical damage factor than the 0°-oriented specimens.