Multimaterial design strategies and microstructural characterization of stainless steel 316-Inconel 718 developed by wire-based Directed Energy Deposition

Abstract The combination of different material properties to face severe conditions has been always demanded by different industrial sectors. For instance, in gas turbine components, excellent mechanical properties at high temperatures and corrosive environments are required. Traditionally, this has been achieved by conventional manufacturing of multiple materials with several steps and joining processes. However, manufacturing the entire component within the same process by additive manufacturing and the combination of two different materials is presented as a potential via to explore. In this research, the additive manufacturing of stainless steel (SS316L) and Nickel-based Inconel superalloy (IN718) multimaterial through different design strategies approaches has been developed and investigated by wire-based Laser Directed Energy Deposition (DED) technology. Direct transition between materials was applied and three multimaterial sandwich structures (S1, S2 and S3) were designed and successfully manufactured. The microstructure obtained in the three different regions (IN718, IN718/SS316 and SS316) was evaluated in both XY and XZ build directions. Rockwell C hardness was measured along the cross-sections of all samples to compare the different properties of the three samples developed. Defective microstructural features like big porosity, cracks or lack-of-fusion at the SS316/IN718 interphases were not evidenced for S2 and S3 strategies. Multimaterial samples showed very fine microstructures corresponding to the DED processing, and secondary phases such as intermetallic-compounds or carbides were not found. Smooth transitions between materials were obtained which also led to a gradient in microstructure and hardness properties. S3 sample showed the highest hardness value, being the IN718 value even higher compared to conventional IN718 material.