Wire arc additive manufacturing of Inconel 718 inclined thin-walled walls: Inducing the occurrence of multiple fracture behavior of δ phases to significantly improve room-temperature tensile properties

The ease or difficulty of multiple fracture behavior of δ phases is strongly correlated with mechanical properties of Inconel 718 alloy fabricated by wire arc additive manufacturing (WAAM IN718). Considering specific orientation relationship between γ/δ, this study deviated the thin-walled walls from build direction by 0°, 35°, 45° and 55° to control the degree of δ phase fracture during tensile tests. By applying different heat treatment processes to thin-walled walls with various inclinations, this study aims to verify the universality of the aforementioned hypothesis across the δ phases with different morphologies, thereby providing fundamental theoretical support for the hypothesis. The experimental results indicated that multiple fracture behavior of δ phases became easier with increasing inclination angles, which led to the progressively higher tensile strength of WAAM IN718. Based on the simplified grain model, δ phases with slender morphology continuously distributed along columnar grain boundaries were more prone to multiple fracture behavior under external loading perpendicular to grain boundaries. Different from slender δ phases at grain boundaries, this study innovatively found that the intragranular uniformly distributed lamellar δ phases tend to grow along the (-1-11)γ plane trace, and multiple fracture behavior always occurs preferentially in those δ phases grown along the (-1-11)γ plane trace. This study provides powerful experimental support and theoretical basis for the recently proposed secondary strengthening phenomenon of δ phase, which is expected to use this phenomenon to design a new post-treatment scheme in subsequent work to further improve the strength and plasticity of WAAM IN718 alloy.