Effect of build orientations on residual stress, microstructure, and mechanical properties of additively manufactured alloy-718 components

During the laser powder bed fusion(L-PBF) process, the rapid solidification conditions coupled with repeated heating and cooling cycles constrain the design potential and printability of complex-shaped structures, especially for part-scale components. Process-induced residual stress, porosity, and crystallographic texture are the most challenging obstacles when designing quality components using this process. These defects also have a detrimental impact on the quality and structural durability of the deposited parts. To comprehend the coupled effect of these determinants on the mechanical performance of various orientated components, we perform a sequentially coupled thermo-mechanical simulation to obtain the residual stress evolution during the deposition as well as on printed coupons after the extraction of the support structure. Simulated outcomes have been verified using X-ray diffraction, and there is a good convergence between simulated and experimental values with a 10% maximum difference. X-ray tomography and Electron back scattered diffraction(EBSD) techniques were utilized to quantify the process-induced porosity(distribution and size) and crystallographic texture in the solidified component, respectively. The mechanical performance of the deposited components was evaluated using uniaxial tensile tests. The cracking behavior in fractured samples was studied using SEM-based fractography. Due to more number of repeated thermal cycles, the vertically deposited sample had higher residual stress, larger grains, and thus lower strength.