Interfacial Stability of Additively Manufactured Alloy 625–GRCop-42 Bimetallic Structures

This study examines the diffusion behavior, thermal stability, and mechanical properties of the bimetallic interface between additively manufactured copper alloy GRCop-42 and nickel alloy 625 (UNS N06625) following elevated temperature exposure at service-relevant conditions for high-temperature superalloys. The copper alloy was additively manufactured using laser powder bed fusion. The nickel alloy was subsequently deposited directly onto the copper alloy using powder-based directed energy deposition. The samples were held at a temperature of 816 °C (1500° F) for varying exposure times between 50 and 500 h. Significant material loss (averaging ~430 at 50 h and ~1830 at 500 h) due to oxidation was noted in the copper alloy. The bondline interface was examined using optical microscopy as well as electron microprobe analysis. Composition maps from the electron microprobe showed the formation of oxides in the copper alloy and Laves phase in the nickel alloy at thermal exposure times of 200 h or more. By analyzing diffusion across the bondline, this study demonstrates the ability of machine learning-based diffusion models to predict diffusion coefficients of copper into alloy 625 () and of nickel into GRCop-42 () and the ability of commercially available diffusion code (Pandat) to provide reasonably accurate diffusion profiles for this system. Tensile and fatigue tests were performed in the as-built and 200 h thermal exposure conditions. The thermally exposed samples exhibited an average 18.6% reduction in yield strength compared to the as-built samples.