Effect of Heat Treatment on the Microstructure and Properties of Inconel 718 Alloy Fabricated by Selective Laser Melting

Inconel 718 alloy was fabricated by selective laser melting (SLM) and treated with different solutions and two-stage aging heat treatments (H1-H4). The microstructure evolution of the alloy under four different heat treatments was analyzed, and the influence of the size and quantity of precipitates on the mechanical properties of the alloy under different aging mechanisms was explored. The results showed that after solution treatment at 1020 °C, the structural segregation at the boundaries of columnar and equiaxed crystals disappeared, the Nb-rich Laves phase and carbides were dissolved into the matrix. After aging treatment, γ′ and γ″ strengthening phases were precipitated in the matrix, and the fine needle-like γ″ phase was uniformly distributed, which played the role of dispersion strengthening and significantly improved the strength of the alloy. Under the double aging system of 720 °C + 620 °C (H4), the average size of precipitates was 26.47 nm, and the properties of the alloy tend to be isotropic. After H4 heat-treated, the σUTS and σ0.2 of the sample reached 1520 MPa and 1272 MPa, respectively. There was no obvious fracture and spalling on the worn surface of the alloy, thus it showed good friction and wear resistance. At the same time, it was proved that the temperature change at the first stage of double aging had a greater influence on the precipitation of the strengthening phase than that at the second stage.