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

Abstract

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.

Effect of pre-heating and post-weld heat treatment on structure and mechanical properties of laser beam-welded Ti2AlNb-based joints

“…Upon pre-heating to 600 • C, the weld exhibited a yellowish tint (Fig. 4c) that is considered acceptable for welded joints [27]. However, the purple color of the welds after welding with pre-heating to 800 • C indicated severe oxidation (Fig.…”

“…5): the fusion zone (FZ), the heat-affected zone (HAZ), and the base metal (BM). According to Liu et al [29] and Wang et al [27], the FZ possessed the hourglass-shaped cross-section due to more significant melting (less efficient heat dissipation) in the upper and lower part compared to the middle part. FZ predominantly consisted of the β-phase.…”

Pulsed Laser Welding Applied to Metallic Materials—A Material Approach

“…Since the pulsed joint of Ti3Al-Nb alloy displayed pores associated with the Al evaporation in the FZ, Nb was applied as a filler material and avoided the formation of these defects (Figure 12I,J) [78]. A non-uniform weld zone was created with a white region (NbTi solid solution) and a grey region with columnar crystal and dendrite structure.…”

“…Moreover, Ti-5Al-2.5Sn joints showed a considerable fined aspect of this phase (Figure 12A,B) [75]. In the case of Ti-2Al-1.5Mn alloy (Figure 12C-E), the HAZ displayed 2 distinguished sub-zones: partially or fully Pulsed laser weldments made of titanium: Ti-5Al-2.5Sn FZ (A) and HAZ (B) [75]; Ti-2Al-1.5Mn (C), its FZ (D) and HAZ (E) [76]; Ti49.4Ni50.6 TiNi (F), its FZ (G) and HAZ (H) [77]; Ti3Al-Nb (I) and Ti3Al-Nb with pure Nb filler metal (J) [78]. Pulsed laser weldments made of titanium: Ti-5Al-2.5Sn FZ (A) and HAZ (B) [75]; Ti-2Al-1.5Mn (C), its FZ (D) and HAZ (E) [76]; Ti49.4Ni50.6 TiNi (F), its FZ (G) and HAZ (H) [77]; Ti3Al-Nb (I) and Ti3Al-Nb with pure Nb filler metal (J) [78].…”

“…Figure 12.Pulsed laser weldments made of titanium: Ti-5Al-2.5Sn FZ (A) and HAZ (B)[75]; Ti-2Al-1.5Mn (C), its FZ (D) and HAZ (E)[76]; Ti49.4Ni50.6 TiNi (F), its FZ (G) and HAZ (H)[77]; Ti3Al-Nb (I) and Ti3Al-Nb with pure Nb filler metal (J)[78].…”