Effect of various combinations of Ti and Zr interlayers on the tensile properties of laser welded joints of molybdenum

Molybdenum (Mo) is of great potential in the nuclear energy field, however, the embrittlement and the lower tensile strength limit the application of the fusion welded joints. Titanium (Ti) and zirconium (Zr) were synchronously added into the fusion zone (FZ) to improve the tensile strength and certain ductility of laser beam welding joints. By utilizing high-resolution scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and nanoindentation, the microstructures and mechanical properties of FZs in the joints under different alloying strategies with Ti and Zr were analyzed. Zr is mainly present in Mo as Mo2Zr, playing the second-phase strengthening effect; Ti is mainly present in Mo in an atomic state, playing a role of the solid - solution strengthening. The addition of Ti and Zr with different mass proportions can control the relative contents of Mo2Zr phase and solid - solution atoms in the FZ, control the distribution of zigzag and flat grain boundaries and influence the relative distributions of low - angle grain boundaries (LAGBs) and high - angle grain boundaries (HAGBs). In the end, combined addition of Ti and Zr is possible to improve the tensile strength while decrease the loss of ductility of the joint.