Understanding the Mixing in the Inconel–GRCop-42 Interface Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) enables fabrication of complex bimetallic structures, such as combustion chambers, that require a thermally conductive internal liner supported by a high-strength structural jacket. Inconel 625 (IN625) served as the substrate, with GRCop-42, a Cu-Cr-Nb alloy developed by NASA Glenn Research Center, deposited with varying laser powers and laser scanning speeds to create the IN625–GRCop-42 interface. Hot isostatic pressing (HIP) was performed to evaluate defect mitigation, and Vickers microhardness testing was conducted to assess the mechanical properties across the bimetallic interface. Microstructure characterization revealed porosity across the full processing window and, along with density measurements, we were able to establish that the HIP treatment was unsuccessful in eliminating the defects, indicating that densification is primarily achieved by LPBF process optimization. Microhardness testing showed that the as-printed samples showed higher microhardness values than the as-HIPped samples due to the fine microstructure, high dislocation density and residual stresses caused by the LPBF process. The decrease in microhardness following HIP suggests that recrystallization, grain coarsening and residual stress relief may have occurred during post-processing. These results highlight the importance of LPBF process optimization in achieving strong, thermally stable IN625–GRCop-42 bimetallic interfaces. This study investigates the microstructural and mechanical behavior of the IN625 and GRCop-42 dissimilar metal interfaces fabricated using the LPBF process and the effects of HIP on the bimetallic microstructure.