Fracture Patterns of Nickel Alloy Obtained by Wire Feed Electron Beam Additive Technology under Tension, Fatigue and Creep

Abstract Wire-feed electron beam additive manufacturing (WEBAM) is a highly efficient method for fabricating large-scale aerospace components from nickel and copper alloys. This study presents a comprehensive investigation into the microstructure and failure mechanisms of experimental specimens of the high-temperature Inconel 718 superalloy and Ni-Cu functionally graded bimetallic materials fabricated via WEBAM. For the Inconel 718 alloy, a critical anisotropy in high-temperature creep behavior was revealed. When loaded along the build direction (parallel to the dendrite axes) at a stress of 550 MPa and a temperature of 700 °C, the time to rupture was 4.7–6.0 hours, exhibiting a mixed ductile-intergranular fracture morphology. Conversely, when loaded along the scanning direction (perpendicular to the dendrite axes), the rupture life catastrophically decreased to 0.2–0.4 hours—a 15- to 30-fold reduction. Fractography demonstrated that the failure occurs via intergranular (interdendritic) decohesion along the interdendritic regions enriched with carbide-forming elements (Cr, Nb, Mo), which act as weakened interlayers at elevated temperatures. At room temperature, during uniaxial tensile and low-cycle fatigue tests, this factor does not significantly affect the strength characteristics. The obtained results prove the necessity of accounting for the dendritic structure orientation when designing components operating under high-temperature creep conditions and are of great importance for optimizing the manufacturing technologies of critical aerospace parts.