Effects of in-process LN2 cooling on the microstructure and mechanical properties of Type 316L stainless steel produced by wire arc directed energy deposition

For the first time, in-process cryogenic cooling for Wire Arc Directed Energy Deposition (DED) and its influence on the microstructure and mechanical properties of Type 316L stainless steel is investigated. The in-process cryogenic cooling is applied with a liquid nitrogen cryogenic jet positioned behind the welding torch, targeting the material directly behind the melt pool during deposition. Compared with Wire Arc DED that is conducted with a regulated interpass temperature of 160°C, the crystallographic grain orientations of the deposit with in-process LN2 cooling were found to be significantly more random, with high numbers of equiaxed grains generated. For the samples produced using in-process cryogenic cooling, the tensile tests resulted in a mean Young’s Modulus of 163 ± 51 GPa. This is significantly higher compared with samples produced using interpass temperature control which resulted in a mean of 72 ± 27 GPa. BS EN 10088-1 guidance for Type 316L specifies a Young’s Modulus of 200 GPa. The stiffness improvement with in-process cooling demonstrated in this research is a significant finding for the additive manufacture of parts by Wire Arc DED for structural applications in the architectural and nuclear industries.