Regulation of performance of laser-welded socket joint of Mo-14Re ultra-high-temperature heat pipe by introducing Ti into both weld and heat affected zone

Fusion welding of molybdenum (Mo) alloys faces problems including grain coarsening and embrittlement, so that the obtained joints have poor mechanical performance. The research took the socket joints of a novel Mo-14Re ultra-high-temperature (UHT) heat pipe as research objects. Pre-heating, titanium (Ti) microalloying and brazing were adopted for coordinated regulation of defects, microstructures, and mechanical performance of joints. Results show that Ti added can be uniformly mixed with metals in the molten pool and solidly dissolved in the matrix to achieve solid-solution strengthening. Ti entering the weld zone distributes on grain boundaries and in grains, thus decreasing the relative content of Mo oxides on the surface of grain boundaries in the meanwhile of grain refinement, playing a role in purifying grain boundaries. Ti alloying in the weld zone to some extent can inhibit occurrence of pore defects and improve the bearing capacity of joints. Moreover, the brazing layer formed in the heat affected zone (HAZ) not only enlarges the bonding and bearing area of joints, but also shifts the position of the stress concentration point of joints from the near weld zone with poor performance to the area with favorable performance much farther from the weld. Under the joint action of Ti microalloying and brazing, the tensile strength of joints is improved from 140.8 to 399.8 MPa. The fracture mode changes from intergranular fracture to transgranular cleavage-like fracture. The research results can promote the development of technologies for manufacturing novel UHT heat pipes and welding Mo-Re alloys.