Synergistic strengthening effects of solid solution and second phase in vacuum laser welded joint of Mo alloy with Ti addition

Titanium (Ti) element has been proven to enhance the tensile strength of molybdenum (Mo) alloy welded joint and its strengthening effect was only attributed to solid solution strengthening. Nonetheless, a more detailed understanding of this mechanism was required. In this study, the Ti foil was used to regulate the Mo alloy laser welded joint under the vacuum environment and the tensile strength reached up to 469 MPa, which was the maximum value available. Furthermore, synergistic strengthening effects of solid solution and the second phase on Mo-Ti welded joints were proposed. Solution strengthening contributed 334.1 MPa to the improvement of tensile properties. It was attributed to a 31.3% reduction in lattice size, accompanied by respective increases of 10.8% and 8.7% in Young's modulus and shear modulus. Besides, the anisotropy of Young's modulus and shear modulus decreased and the lattice stability increased. Additionally, the second-phase strengthening provided 146.8 MPa strengthening contribution through the dispersed distribution of TiO 2 particles in the molybdenum matrix, effectively hindering the extension of cracks at the grain boundaries. The quantified mechanism validated the synergistic interaction between these complementary strengthening pathways. This study deepens the understanding of the strengthening mechanism of Ti on Mo alloy welded joints and further widens the application of Mo alloys.