Quantification of location-dependence in a large-scale additively manufactured build through experiments and micromechanical modeling

Wire-based directed energy deposition additive manufacturing techniques (AM) permit the rapid production of large-scale structural components which are not currently possible using the more common powder bed fusion (PBF) AM methods. However, due to larger melt pool widths and higher energy inputs than PBF methods, local thermal history effects produce significant location-dependent microstructure, porosity, and mechanical behavior that necessitates thorough quantification of this emergent technology. Wire + Arc Additive Manufacturing (WAAM) was used to produce austenitic stainless-steel single bead walls in order to statistically quantify the variation of critical material properties within the build. Individual grain geometric properties evaluated using electron back scatter diffraction at different points in the build were well fit by a three-parameter Weibull cumulative distribution function, yet sufficiently different from averaged values. X-ray diffraction for each location disclosed a strong wire texture in the build direction, leading to anisotropic elastic moduli values that were well described by directionally-dependent modulus predictions obtained from diffraction peak analysis. Location-dependent mechanical behavior was examined and accurately captured by an elasto-viscoplastic model based on the Fast-Fourier Transforms (EvpFFT) using the local microstructure orientation data as input. Overall, a high-quality build was realized, with minimal porosity of less than 0.32%, and median yield and tensile strength values of approximately 320.4 ± 8.0 MPa and 531.6 ± 8.2 MPa, respectively. In conclusion, mean values for mechanical behavior within the wall build were found to closely resemble single pass weldments, with statistical variation between individual locations mainly occurring in the weld direction due to local thermal history effects.