Laser seal welding of end plug to thin-walled nanostructured high-strength molybdenum alloy cladding with a zirconium interlayer

The effects of micro-alloying method on microstructure and properties of laser-welded molybdenum alloy joints were investigated, and zirconium was selected as the additive material. In the fusion zone of the joint without zirconium addition, the segregation of MoO₂ on the grain boundary were observed, leading to the brittle fracture of the joint. When zirconium ring was added into the fusion zone, ZrO₂ was preferentially formed in the grain interior which alleviated the segregation of MoO_2. The grains at fusion zone were refined under the effect of heterogeneous nucleation particles of ZrO₂, thus it changes the fracture mechanism of welded joint from intergranular fracture to cleavage fracture. When zirconium foil was pre-placed at the overlapped interface of cladding tube and the end plug, a parasitic brazing zone was generated due to the high melting point and high thermal conductivity of molybdenum. Tensile strength of the welded joints matched that of the base metal. These results highlight possibilities for achieving high strength joints when joining refractory materials with intrinsic brittleness in complex joint configurations.