Effect of Layer Addition on Residual Stresses of Wire Arc Additive Manufactured Stainless Steel Specimens

Abstract

Residual stresses have been characterized in four Wire Arc Additive Manufacturing specimens with neutron diffraction technique. First, two methods are investigated for obtaining the reference diffracted angle θ0 that is required for the computation of microstrains and, thus, the stresses; θ0 was obtained with two approaches. The first one required a strain-free specimen in order to get directly the reference diffracted angles θ0 in the three principal directions. The second one is based on the plane stress assumption to get θ0 indirectly by imposing that the normal stress was equal to zero. Both methods led to similar residual stress profiles for the one-layer specimen which validated this approach for all specimens without a strain-free specimen available. The second part of this work focused on the modification of the residual stresses in the specimen following the addition of a new deposit. The neutron diffraction measurements showed that the longitudinal stress was tensile in the heat-affected and fusion zones with a maximum value located at the parent material–layers interface where the thermal loadings were applied. A decrease of this maximum value from 257 MPa to 199 MPa appeared after deposition of a new layer which is due to some stress relaxation effect. Inside the parent material, a large zone presents compressive longitudinal stress up to −170 MPa. The bottom part of the parent material is under tensile stress likely due to its upward bending following the thermal contraction of the deposited layers during cooling to ambient temperature.