Effects of in-process LN_2 cooling on the microstructure and mechanical properties of type 316L stainless steel produced by wire arc directed energy deposition

摘要

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 degrees 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. Crown Copyright (C) 2020 Published by Elsevier B.V. All rights reserved.