Effects of intermediate layer on interfacial microstructure and related mechanical properties of Inconel 625 coating on a Cu-Cr-Zr substrate by laser direct energy deposition

Cu alloy/Ni-based superalloy bimetallic systems are widely utilized in aerospace applications owing to their combined outstanding strength and high thermal conductivity. Laser direct energy deposition manufacturing method is usually adopted when preparing this unique system. However, all the existing Cu-Ni alloy systems were usually prepared by directly cladding the Ni alloys without considering the potential intermediate layer to balance the dissimilar physical properties between the Ni and Cu alloys. Here, we have utilized an intermediate layer for cladding Ni-based superalloy on the Cu alloy, trying to improve the interfacial properties and performance of this bimetallic system. The intermediate layer increased the content of Cu at the interfacial region, thus promoting the degree of liquid phase separation and preventing the preferentially solidified Ni-Cr columnar grains from epitaxial growth. It can also induce a large number of micrometer-sized Ni-Cr core-shells, which acted as nucleation sites and led to the further refinement of the grains from 112 to 30 mu m compared to the directly joined samples. Furthermore, the intermediate layer promotes chemical homogenization, reduces the laser power of the directed energy deposition process, and improves the connection strength by reducing the thermal impact on the substrate. The tensile and shear strength of the intermediate layer prepared sample increased by 10.6 % and 21.4 % compared to the directly joined samples, respectively. Therefore, the usage of the intermediate layer can facilitate the improvement in the mechanical properties when processing the bimetallic alloy system.