Multiscale mechanical characterization of 601 nickel-based superalloy fabricated using wire-arc additive manufacturing

The anisotropy in the mechanical properties of 601 nickel-based superalloy fabricated using wire-arc additive manufacturing (WAAM) was investigated through multiscale tensile testing combined with crystal plasticity analysis. Micrometer-scale and millimeter-scale tensile tests were performed to obtain single crystal properties and deformation behavior as the layered structure, respectively. Tensile tests on millimeter-scale specimens, composed of columnar grains grown along [001], exhibited anisotropy in the fracture strain and work-hardening behavior despite the fact that the yield stress was approximately constant regardless of the loading axis. Tensile tests on micrometer-scale specimens, which were single crystals with dendrites, exhibited a critical resolved shear stress (CRSS) of 116 ± 3 MPa. This value was close to 110 MPa for the CRSS of the wire sample without dendrites, which indicates limited influence of dendrite formation on the yielding behavior of columnar grains. Crystal plasticity finite element analysis was carried out to reproduce the experimental deformation behavior depending on the loading direction of the millimeter-scale tensile tests. Based on the numerical results of the simplified analysis models, the possible mechanism of the dependence of loading direction on the deformation behavior is explained by three newly proposed factors related to the Schmid factor of the primary slip system (PSF) for the characterization of non-uniform deformation in multiple crystals. A significant variation difference existed depending on the loading direction, owing to the superposed contributions of the crystallographic orientations and geometrical configurations of the columnar grains.