Residual stresses and distortions in additive manufactured Inconel 718

Direct energy deposition is an additive manufacturing technique, follows layer-wise deposition to avail design freedom and minimizes material wastage. Despite the unique advantages, repeated heating and cooling induces thermal strains in the components. The present investigation is to understand the thermal-induced distortions and residual stresses in Inconel 718 components fabricated through direct energy deposition. The distortions and temperature measurements are carried out in situ and residual stresses are measured using micro-indentation technique. The distortions are increasing with number of layers, and the distortion rate is varying along the height of deposition. The temperature data indicated rapid heating and cooling. The residual stresses measured are compressive in nature, and are approximately 40% of yield strength in magnitude. The ultimate strength, yield strengths are 800 ± 30 MPa, 580 ± 50 MPa respectively, and maximum hardness obtained is 349 HV. Microstructure Characterizations showed continuous growth of columnar dendrites through multiple layers, and Nb segregation at interdendrites.