Effects of Addition of Titanium on Microstructures and Properties of Laser Butt Welded Joints of Mo–30W Alloy

The fusion welding of Mo–30W alloy, a kind of brittle and refractory materials, is still challenging. This study investigated effects of addition of titanium (Ti) on microstructures and properties of laser butt welded joints of Mo–30W alloy. The microstructure, phase distribution and mechanical performance of the welded joint with and without Ti were studied by optical microscope, scanning electron microscope, energy-dispersive spectrometer, electron backscattering diffraction, microhardness tests and tensile tests. The tensile strength of Mo–30W laser welded joint was increased from 108.56 to 409.57 MPa by adding Ti element, reached 58.34% that of base metal. MoO₂ phase and WO₂ phase precipitated at the grain boundary of FZ region of Mo–30W alloy laser butt welded joints without Ti, which significantly reduced the grain boundary strength, resulting in low tensile strength. After the addition of Ti, TiO₂ phase with low Gibbs free energy was formed in GBs (grain boundaries), which reduced the number of MoO₂ phase and WO₂ phase harmful to the GBs strength, therefore, the tendency of grain boundary embrittlement was reduced. The research results can provide reference for laser welding of brittle and refractory metals.