Neutron Diffraction Investigation of Residual Stresses Induced in Niobium-Steel Bilayer Pipe Manufactured by Explosive Welding

Recently, reliable and hermetic joining of stainless steel to niobium pipes has been achieved with the explosive bonding technique. Joining of these two materials are essential to ensure production of a bimetallic transition element of pipe-type for its further use as a part of charged beam acceleration systems of the new generation. A non-destructive neutron diffraction investigation of the tri-axial strains along a radial cross-sectional line through the joint section has been performed. Residual stress results indicate inherently different natures in the residual stress values within the respective pipe sections. In the external stainless steel pipe the residual stresses are tensile, showing a sudden increase to 600 M-Pa as the interface is approached, whilst being compressive in the internal niobium pipe, not exceeding 650 MPa. A characteristic abrupt stress discontinuity exits at the interface region.