Effect of Two-Stage Solution on Microstructure and Mechanical Property of IN718 alloy fabricated by selective laser melting

Abstract The substructure characteristics and mechanical properties of IN718 alloy prepared by selective laser melting (SLM) in the as-deposited state and different solid solution states were studied. The effects of the substructure characteristics, which include the precipitates and grain boundary features, on the microhardness of the IN718 alloy were discussed. It was found that the main substructure of the as-deposited alloy is the cellular structure that is formed owing to the segregation band of Nb and Ti elements with a thickness of 50 nm. The two-stage solution process and single-stage solution process can both correct the microsegregation of the as-deposited state, but the two-stage solution process can make the composition more uniform; at the same time, it leads to a large number of twin boundaries. The δ phase precipitates largely in the single-stage solution process at 980 ℃, but the two-stage solution process can effectively inhibit the precipitation of the δ phase.The hardness of the alloy after two-stage solution is lower than that of the single-stage solution alloy. The main strengthening mechanism of the as-deposited alloy is strain strengthening,The strengthening effect of δ precipitate is lower than the strain strengthening produced by the grain boundary of the alloy.