Microstructures and Mechanical Properties of a Laser-Welded Joint of Ti3Al-Nb Alloy Using Pure Nb Filler Metal

Ti3Al-Nb alloy (Ti-24Al-15Nb) was welded by a pulsed laser welding system without and with pure Nb filler metal. The results indicated that pure Nb filler metal had profound effects on the microstructures and mechanical properties of the laser-welded joints. The joint without filler metal consisted of the weld zone (α’2 + B2), heat affected zone HAZ1 (α2 + B2), HAZ2 (α2 + O + B2) and base metal (α2 + O + B2), and gas pores were generated in the weld resulting in the deterioration of the joint strength (330 MPa) and elongation (1.9%). When the Nb filler metal was used, the weld microstructure (NbTi solid solution + O + B2) was obtained, and the joint properties were significantly improved, which was associated with the strengthening effect of the NbTi solid solution, O phase precipitation and the slip transmission between O and B2 phases, and the restraining of the formation of martensite (α’2) and gas pores in the weld. The strength (724 MPa) and elongation (5.1%) of the joint increased by 119.4% and 168.4% compared with those of the joint without filler metal, and the joint strength was able to reach 81.7% of the base metal strength (886 MPa). It is favorable to use pure Nb filler metal for improving the mechanical properties of laser-welded Ti3Al-Nb alloy joints