Numerical and experimental analysis of the residual stress and microstructure in stainless steel thin-walled components manufactured by wire arc additive manufacturing

Transient thermal loads of Wire Arc Additive Manufacturing (WAAM) cause nonuniform plastic deformation, high residual stresses and high δ-ferrite contents that could negatively impact service life, mechanical performance, dimensional accuracy, and result in failure of material during manufacturing. To control these negative effects, it is vital to understand how residual stress and microstructure form during manufacturing. This study, investigates microstructure and residual stress evolutions during WAAM of AISI 316L thin-walled structures, using numerical and experimental methods. The microstructure was analyzed using optical and scanning electron microscopy. Residual stresses were measured with neutron diffraction and numerically simulated by a thermo-mechanical model. The results show that less than 10% of the microstructure consists of inter-dendritic δ-ferrite, which provides relatively high toughness. The material undergoes a ferrite-austenite solidification mode that is preferred for its lower susceptibility to solidification cracking. The material shows a periodic microstructure due to cyclic material deposition, with equiaxed dendrites at the center of each track with low G/R ratios (6.78 °C∙s/mm 2 ) and columnar and cellular structures close to the bottom and sides of the tracks with significantly high G/R ratios. The highest and lowest residual stresses form perpendicular to the build direction, in the travel and transverse directions, respectively. Residual stresses in the build direction reached 500 MPa in a constrained sample at both ends of the wall, which explains high cracking probabilities in these regions. By changing the WAAM constraint levels, including external clamping and substrate rigidity, residual stress, dimensional accuracy, and failure during production could be controlled.