Thermo-mechanical approach to study the residual stress evolution in part-scale component during laser additive manufacturing of alloy 718

Abstract

Laser Additive Manufacturing (LAM) is a promising technology for manufacturing gas turbine components with enhanced design capability and a significant reduction in part weight. Additive manufacturing of alloy 718 using Laser Powder Bed fusion (L-PBF) process poses certain challenges pertaining to complex residual stress, micro-segregation of Nb, and undesired Laves phase formation in the as-printed state. The built-up residual stress and undesired brittle phase may lead to cracks and build failures. This article studied residual stress evolution during L-PBF of alloy 718 using Finite Element (FE) thermo-mechanical simulation implemented in Simufact Additive® software. The model adopted the bundling of physical powder in voxel mesh to minimize the computational time and mimic the actual process scenario during part-scale simulation. Experimental flow curves generated from Gleeble 3800® tests at elevated temperatures were utilized to calibrate material property for better accuracy in the FE simulation. The calibrated model was used to study the residual stress evolution during support structure removal. Verification and validation of simulated results were performed using X-ray diffraction (XRD) measurements. The simulated value agrees well with the experimental value with a maximum deviation of 7%. Finally, the experimentally validated model was used to correlate the effect of layer thickness variation on residual stress evolution.