High deposition rate wire-arc directed energy deposition of 316L and 316LSi: Process exploration and modelling

Abstract

A parameter design of experiments was undertaken to study the impact of Si content in the wire feedstock, weld speed, and interpass temperature on the microstructure and mechanical properties of high deposition rate Wire-Arc Directed Energy Deposition (WA-DED) of 316L stainless steel. Small-scale, representative builds were constructed using a high deposition rate pulsed spray transfer mode. Across conditions, WA-DED 316L builds exceeded American Society of Mechanical Engineers (ASME) SA-240 minimum values for yield strength, elongation, and tensile strength at room temperature, tested both parallel and perpendicular to the build direction. It was found that 316LSi samples (higher Si content version of 316L) displayed significantly higher strengths and ductilities than samples produced with 316L, while the impact of weld speed and interpass temperature were less significant. A heat transfer model of the WA-DED process was created to allow for microstructure predictions. An infrared thermal camera system was used to calibrate this model by taking temperature measurements at fixed points during the deposition of several layers. Solidification models were developed to allow for predictions of microstructural features in the as-built condition. Predictions of dendrite spacings and growth morphologies show good agreement with experiments, demonstrating the potential for modeling the influences of the WA-DED parameters for process optimization. Based on microstructural analysis, it was concluded that the increase in strength and ductility in 316LSi compared to 316L is due to effects of composition on solid solution strengthening and stacking fault energy, suggesting opportunities for developing new stainless steel alloys for WA-DED with improved mechanical performance.