Effect of solution treatment on microstructure and stress rupture properties of precipitation hardened IN718 superalloy fabricated by laser powder-bed fusion process

Abstract

Effect of solution temperature in precipitation hardening on microstructure and stress rupture properties of IN718 superalloy fabricated by laser powder-bed fusion (LPBF) process is investigated. The LPBF samples were solution treated at 980, 1060 and 1130 °C, followed by two-step aging at 720 and 620 °C, each for 8 h. The results showed that the solution treatment at 980 °C was not suitable for stress rupture properties due to the formation of δ and Laves phases along grain boundaries, which promoted intergranular fracture. On the other hand, non-uniform grain growth occurred in the sample solution treated at 1130 °C, which reduced stress rupture properties. The solution treatment at 1060 °C was found more suitable to improve stress rupture behavior of the LPBF IN718 superalloy at 650 °C. The rupture life of the alloy approached 87 h due to the formation of suitable grain structure and distribution of γ′/γ″ strengthening phases.