Microstructures and mechanical properties of electron beam welded CuCrZr/Inconel/316L tube-to-tube junctions for WEST project

Abstract The microstructures and mechanical properties of electron beam welded CuCrZr/Inconel/316 L junctions for WEST project have been investigated. As the welding of ending tubes is performed after the hot isostatic pressing (HIP) for the real components, in this study the CuCrZr tubes were annealed with identical parameters of HIP before welding in order to simulate the real situations of component manufacturing. The junctions were free of defects such as micro-cracks or incomplete penetration. The mechanisms of macro-segregation features, such as beaches, peninsulas, and irregular islands, and of micro-segregation features, such as small spheres, dendrites, Cu-rich particles, and Nb/Mo-rich networks have been discussed. Mechanical testing shows that postweld aging nearly does not improve the tensile strength of the junctions because it just shifts the weakest point of CuCrZr slightly away from the Inconel/CuCrZr weld, but it is beneficial for the tensile elongation of the junctions at 200 °C; meanwhile, postweld aging decreases the hardness of CuCrZr in regions out of the heat affected zone. Cold helium testing performed after rotary fatigue testing indicated that postweld aging does not change the fatigue resistance of the junctions, at least under the current testing conditions. Significant increments in hardness of irregular Inconel-rich islands induced by aging may be attributable to the formation of Nb/Mo-rich networks. This study may be of significance for the manufacturing of ITER divertor components.