Isothermal Solid‐State Transformations of Inconel 718 Alloy Fabricated by Selective Laser Melting
Wenpu Huang, Zemin Wang
Abstract
Inconel 718 samples have been fabricated by selective laser melting (SLM) and subjected to a series of heat treatments to study the isothermal precipitation behaviors of δ, γ′, and γ″ phases. A time–temperature–transformation (TTT) diagram for as‐built Inconel 718 is finally plotted. The morphology, size, and distribution of δ phase are studied, and the corresponding transformation kinetics is analyzed by Avrami equation. The results demonstrate that the transformation rate at 900 °C is the highest, though the nose of the TTT curve occurs at 860 °C after an incubation period of 10 min. As the aging temperature increases (620–820 °C), the precipitation rate of γ′/γ″ increases and the time to reach peak hardness decreases. The nose of the TTT curve for γ′/γ″ precipitation occurs at 820 °C after only 32 s. Nevertheless, when aged above 720 °C, the peak hardness decreases. In addition, the age hardening can be described by Avrami equation when δ phase is absent (620–770 °C). In summary, SLMed Inconel 718 exhibits a faster precipitation kinetics compared with wrought material, whereas their phase transition temperatures are similar.