Effect of solution treatment on microstructure and stress rupture properties of precipitation hardened IN718 superalloy fabricated by laser powder-bed fusion process
A. M. Chizari, A. Kermanpur, Ehsan Foroozmehr, Ahmad Rezaeian, Fazlollah Sadeghi, Ali Rezaei
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.