Rolling-assisted direct energy deposited Inconel 718: microstructural evolution and mechanical properties after optimized heat treatment

Post-heat treatment is a necessary and important step for additive-manufactured products to relieve residual stress and to further improve mechanical performance. In this work, the heat treatment strategy for Inconel 718 superalloy fabricated by rolling-assisted laser-directed energy deposition (L-DED) has been designed and systematically investigated for the first time. The results show that the designed homogenization heat treatment at 1080 °C for 10 min can effectively dissolve most of the detrimental Lave phases existing in the rolling-assisted L-DED samples. Meanwhile, it results in a homogenous grain structure through static recrystallization, while maintaining a similar prior-refined grain size of ∼8 µm. On this basis, a high number density of γ″ and γ′ precipitates appear in the microstructure after applying a subsequent double-aging heat treatment. The optimized microstructure through such effective post-heat treatment designed in this work has led to a significant increase in material strength at both the room and elevated temperatures while maintaining good ductility.