Niobium-316L Stainless Steel Transition Joints for Superconducting Radiofrequency Cavities by Explosive Welding

Abstract:

The study of the manufacture of niobium/316L stainless steel transition joints can lead to a new breakthrough in improving the material for the helium vessel of the superconducting radio frequency cavities. In this study, 316L stainless steel and niobium composite plates were fabricated by explosive welding technique. Microstructure and mechanical properties of the composite plates were investigated both immediately after explosive welding and after heat treatment processes. The investigation of microstructure demonstrated that no brittle intermetallic layer was formed and no diffusion phenomenon was observed after heat treatment processes. Mechanical tests including tensile tests, shear tests and bending tests were conducting both at room temperature and cryogenic temperature. At low temperature, the composite plates held higher strength than at the room temperature. In cryogenic tensile tests, we observed that the Niobium section of the composite plate broke in layers when the sample reached yielding strength. Beside the raw material, transition joints with Nb-SS adapters were designed and fabricated. The leak check showed the joints’ leak rates meet project requirements and indicated explosively bonded Nb-SS is viable way to fabricate stainless steel helium vessel for SRF cavities.