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

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

Influence of process parameters in powder bed fusion of 316L steel: A residual stress study

To maintain the structural integrity in additively manufactured samples, it is important to study the induced residual stresses which are widely ignored. Powder bed fusion (PBF) is a type of additive manufacturing process in which the metal powder is added to a substrate, step by step. Scanning parameters including layer thickness, overlap percentage, the angle between layers and scanning strategy that can be controlled in this process lead to different mechanical properties, microstructures, and residual stresses. This study compares the effects of layer thickness, overlap percentage, and the angle between layers on residual stresses. For this purpose, several specimens with different process parameters were made from 316L steel powder, using PBF, and the residual stresses were measured by incremental centre hole drilling method. Furthermore, residual stresses induced in powder bed fusion technique were also assessed numerically. It was observed that the overlap percentage showed more impact among other parameters. It was also addressed that manufacturing parameters should be carefully selected to minimize the magnitude of residual stresses as they can affect the residual stresses field simultaneously. Experimental and finite element results showed a good agreement