Effect of laser power and deposition sequence on microstructure of GRCop42 - Inconel 625 joints fabricated using laser directed energy deposition

The joining of Inconel 625 and GRCop42 using additive manufacturing is required for thermal management of high operating temperature components such as rocket combustion chambers. Though prior efforts have been made to use laser directed energy deposition to join these materials, the impact of laser power and deposition sequence on microstructure of these joints is not well understood. In this study, Inconel 625 onto GRCop42 and GRCop42 onto Inconel 625 joints are fabricated by powder directed-energy-deposition at various laser powers and subsequently subjected to characterization in terms of present defects, grain morphology, and phases. Results show lack-of-fusion free Inconel 625 onto GRCop42 joints can be fabricated by increasing the laser power in the first layer. Substrate remelting in GRCop42 onto Inconel 625 joints is found to result in a melt pool composition which induces liquid-state immiscibility, resulting in a Cu-deprived liquid solidifying to form crack prone islands. Increasing laser power decreases the embrittlement of these islands due to the precipitation of a lower volume fraction of intermetallic phases.