Influence of plasma narrow-jet cutting parameters on the weld quality during laser welding of titanium alloys

The study investigates the structural and mechanical characteristics of permanent joints produced by laser welding of VT1-0/VT1-0 titanium alloys after cutting with a newly designed PMVR-5.3 narrow-jet plasma torch, which features a gas-dynamic stabilization (GDS) system with several design innovations. The improved GDS efficiency enhances cutting precision and surface quality, thereby increasing the radiation absorption coefficient, weld penetration, and overall laser-welding efficiency. Experimental results show that continuous-wave CO2 laser welding of VT1-0/VT1-0 plates forms a narrow weld with a structure corresponding to the as-cast state of the alloy and large equiaxed grains in the central part of the weld, which decrease in size toward the root compared with those in the surface region. Although gas shielding does not completely prevent the formation of fine micropores in the weld metal, their amount is insignificant; they do not form critical clusters within the microvolumes of the weld and have no adverse effect on the strength characteristics of the welded joint. The average microhardness of the weld metal was found to be higher than that of the base metal. According to tensile and microhardness testing, the weld metal demonstrates high strength, significantly exceeding that of the titanium alloy, and exhibits a ductile fracture morphology. Under cyclic loading, fracture occurred in the base metal rather than in the weld metal, with the fraction of the final rupture zones increasing as the maximum cyclic stress rose. The findings confirm the applicability of precision narrow-jet air-plasma cutting and continuous-wave CO2 laser welding technologies for producing VT1-0/VT1-0 welded joints with high efficiency and mechanical strength comparable to those of the base material.