Copper alloy–stainless steel bonded laminates for fusion reactor applications: tensile strength and microstructure

The tensile strength of copper alloy–stainless steel bi-layer panels joined by hot isostatic pressing or explosive bonding was tested over a temperature range 25–350°C. The bonding processes caused changes in interfacial microstructures which affected the interfacial mechanical properties. Hot isostatic pressed materials studied included: precipitation strengthened CuNiBe or dispersion strengthened Cu–Al2O3 bonded to 316L stainless steel plates and Cu–Al2O3 bonded to Cu–Al2O3. An explosive bonded panel of Cu–Al2O3–316L stainless steel was also examined. Hot isostatic pressed panels showed similar decreasing shear strengths with increasing temperature, while the explosive bonded panel displayed substantially higher strength at 25°C but declined rapidly as the test temperature increased. Tensile strengths of all panels were nominally lower than the constituent bulk material strengths and delamination near the copper alloy–stainless steel interface was the dominate failure mode in the bi-metallic panels. The joining processes were found to alter the microstructure of the bond interfacial regions in the form of microporosity and Fe–Cr–B precipitate formation, NiBe precipitate morphology changes and interdiffusion of constituent elements.