The effects of graphene content on the mechanical properties and thermal conductivity of Inconel 718 superalloy brazed using BNi-2/graphene composite filler metal

•Suitable graphene content in filler metal can enhance strength of Inconel 718.•Added graphene, the intermetallic compounds disappeared in welding area.•The added graphene can enhance the thermal conductivity of weldment. The graphene/BNi-2 filler composites (G-BNi-2) with different graphene contents were used to braze Inconel 718 superalloy in a vacuum furnace. The wettability between different graphene contents of composite G-BNi-2 filler and Inconel 718 superalloy were analyzed after brazing, and all the contact angles of composite filler with different graphene contents on Inconel 718 were lower than 70°, indicating that all the BNi-2 filler and G-BNi-2 composite fillers have good affinity with the Inconel 718. The typical interfacial microstructure of the brazing samples and the formed intermetallic compounds are analyzed with EDS, SEM, XRD and TEM. The effects of the graphene content on the microstructure of brazing area and mechanical properties such as microhardness and shear strength were investigated. The shear strength of brazed sample using BNi-2 filler was approximately 378.9 MPa. The highest shear strength of 390.8 MPa was achieved for brazed specimen using G-BNi-2 composite filler with 0.03 wt% graphene. However, above this graphene content, the shear strength progressively decreases as the graphene content increases. The highest thermal conductivity of 22.7 W/m·K was achieved for brazed sample using the composite filler with the highest graphene content (0.07 wt%).