Comparison of tensile and LCF behaviour of heat-treated Inconel 718 printed by LPBF and LW-DED at different temperatures

This study investigates the effect of processing routes on the tensile and low-cycle fatigue (LCF) performance of Inconel 718 at room temperature (RT) and elevated temperatures fabricated via Laser Powder Bed Fusion (LPBF) and Laser Wire Direct Energy Deposition (LW-DED) under identical heat treatment conditions. Despite the contrasting differences in the solidification microstructures, including dendritic arm spacing, grain size, and the size of secondary phases, the as-printed tensile and LCF behavior of both routes remained comparable. On the contrary, heat-treated LPBF samples exhibited significantly better mechanical properties than LW-DED conditions due to the influence of printing signatures. Among all conditions, LPBF-STA demonstrated the highest tensile strength and LCF performance, surpassing wrought Inconel 718. In contrast, while the LW-DED-STA exhibited good tensile strength and ductility, it demonstrated a significantly poor LCF performance, especially at 650°C. The cyclic softening in the STA samples was due to a combined variation in both back stress and friction stress, attributed to the reduction in the size of γ’’-precipitates. The work reveals the similarity and contrast in the mechanical properties of two processing routes in the as-printed and heat-treated conditions, respectively, and provides insights that are helpful to design Inconel 718 components.