Additive manufacturing of functionally graded inconel 718: Effect of heat treatment and building orientation on microstructure and fatigue behaviour

This paper addresses the effect of post-process heat treatments on microstructure and fatigue crack growth behaviour functionally graded (FG) laser powder bed fusion (L-PBF) Inconel 718 (IN718) superalloy. Sets samples were additively manufactured (AM) altering process parameters, namely power, scanning speed, layer thickness, hatch distance, beam distribution function, resulting in distinctly different microstructures. Two categories underwent treatment (HT) hot isostatic pressing followed by HT (HIP+HT), while one category was kept as-processed (AP) condition to reveal effects post-treatments. Additionally, study microstructural anisotropy, printed horizontal (H) vertical (V) building directions. To better understand FG materials, non-graded (NG) L-PBF wrought material investigated as references. Significant variations terms porosity, grain size elongation, crystallographic texture, content strengthening precipitates or detrimental phases found AM groups. The NG materials also studied conducting three-point bending tests. Findings role microstructures fatigue-crack initiation rate are presented discussed for all samples. demonstrated that can enhance damage tolerance IN718 level material. Interestingly, roughness induced closure be a function build orientation, especially low stress ratio regime.