<i>In Situ</i> microstructure control during electric-arc-directed energy deposition

Electric-arc-directed energy deposition (Arc-DED) revolutionises 3D metal printing by overcoming powder-based processes’ size and production rate limitations. While powder-based processes are constrained by small build chambers and 3–30 micron layer heights, Arc-DED allows for unlimited build scales and 3 mm layer heights, achieving up to 100 times faster deposition rates. Unfortunately, the high energy needed for these rates and thicknesses intensifies the heating and cooling cycles inherent to Arc-DED. This causes significant variations in microstructural and mechanical properties, limiting its use for advanced alloys. This study introduces a conformal top cooling method to regulate the chaotic thermal environment of Arc-DED deposition and produce as-deposited Inconel 718 (IN718) material equivalent to the solutionized condition. The concept is experimentally investigated using cold metal transfer (CMT) of IN718. The role of microstructural and phase uniformity during material production is discussed, material performance in as-deposited and heat-treated conditions is evaluated, processing-property relationships are investigated, and applicability to other materials is addressed. Results show a 45% reduction in process time due to improved thermal management, translating to as-processed microstructural uniformity. Homogeneity in grain growth, controlled phase development, and mechanical testing suggest an as-processed solutionizing effect, with minimised impact of specimen orientation after heat treatment.