Mechanical property heterogeneity in Inconel 718 superalloy manufactured by directed energy deposition

Powder-based laser-directed energy deposition (L-DED) enables rapid prototyping and production of complex geometry Inconel 718 parts for structural applications. However, the heterogeneous microstructure obtained by the L-DED could lead to non-uniform mechanical properties at room temperature. Therefore, evaluating the local heterogeneity in mechanical properties of L-DED manufactured Inconel 718 superalloy is important. The mechanical properties in terms of hardness and local tensile properties of Inconel 718 superalloy have been investigated within the sample volume manufactured by L-DED to determine the local variations in properties. The mechanical properties were compared under the as-deposition and standard solution treatment and aging (STA) conditions. The average hardness and tensile strength properties of L-DED Inconel 718 in as-deposition conditions were significantly lower, while the strain-to-failure is significantly higher than that of its wrought counterparts. STA leads the average mechanical properties of L-DED Inconel 718, which is equivalent to its wrought counterpart. The hardness varied along the deposition direction in as-deposited L-DED Inconel 718. Interestingly, the local variability in the hardness along the deposition direction in L-DED Inconel 718 was eliminated after STA. The tensile strength properties varied along the deposition direction and were found to be lowest near the surface. The local variation trend in tensile strength properties was the same even after STA. The local ductility followed a trend relative to the strength in L-DED Inconel 718. A careful assessment shows that local variation in the mechanical properties was significant along the deposition direction, while it was minimal along the scanning direction of L-DED Inconel 718 under as-deposition and STA conditions. The local heterogeneity in the mechanical properties in L-DED Inconel 718 is explained in terms of the respective microstructure and deformation characteristics.