3D printing austenitic stainless steel 316L by cold spray process: optimum post-spraying heat treatment conditions

The Cold Spray Additive Manufacturing (CSAM) technique has gained prominence due to its unique non-melting characteristics during the manufacturing process. Whilst cold spray has been extensively employed in research and fabrication of 316L austenitic stainless steel, most of the produced components have been limited to coatings. Although 3D-printed parts have been developed, they often exhibit non-equilibrium microstructures and brittle fracture behaviour in their as-sprayed state. To enhance their mechanical properties, post-spray heat treatment is used. This study delves into the investigation of three critical sintering parameters: heating rate, sintering duration and cooling rate, with a specific focus on their effects on porosity and hardness. The primary objective is to identify the optimal sintering heat treatment conditions for cold-sprayed deposits, with a keen interest in enhancing both mechanical properties and corrosion resistance. In this research, it was found that there was substantial impact of heating rate on porosity formation, attributed to the time required to attain the sintering temperature. Rapid cooling rates prove advantageous in achieving a well-structured microarchitecture devoid of facet grain boundaries and reducing porosity. Conversely, prolonged sintering times do not favour porosity reduction or control of abnormal grain growth (AGG). The culmination of optimal heat treatment conditions, characterised by high heating rates, swift cooling rates and short sintering durations (4 h), has demonstrated a marked improvement in overall material properties. Nevertheless, given the inherent variability in heat treatment processes, deposition techniques, and raw powder materials, a concerted effort is required to standardise result reporting in the existing literature to advance the field effectively.