Understanding the directional deformation and failure characteristics of wire arc additively manufactured Ni-based superalloy using in-situ testing and DIC

Abstract

Ni-based superalloys produced by Wire Arc Additive Manufacturing (WAAM) develop pronounced columnar dendritic grains that extend in the build direction (BD) due to a steep thermal gradient acting opposite to BD, leading to anisotropic mechanical properties. While conventional tensile tests fail to resolve intrinsic crack-tip micro mechanisms, this study employs in-situ tensile testing and Digital Image Correlation (DIC) to investigate directional deformation and failure behaviour in WAAMed Inconel 625. Specimens extracted along and transverse to the BD exhibit distinct microstructural and mechanical responses. The vertical (BD) sample shows columnar dendrites with [001] texture, Nb/Mo segregation, and Laves phases (∼3.57 µm), resulting in lower yield strength (YS: 394 MPa) and ultimate tensile strength (UTS: 675 MPa) but 23 % higher elongation than the horizontal sample. In contrast, the horizontal sample exhibits 31 % higher YS (519 MPa) and 14 % higher UTS (772 MPa), attributed to increased strain hardening and a higher fraction of low-angle grain boundaries (LAGBs: 42 %). DIC reveals higher notch sensitivity in the horizontal sample, while the vertical sample demonstrates rapid strain hardening near yield (9931 MPa vs. 5627 MPa). These findings highlight the critical role of grain orientation and Laves phase distribution in governing anisotropy, providing actionable insights for designing WAAM components for multiaxial loading applications.