Texture characteristics and fracture mechanism of linear friction welded joints of dissimilar titanium alloys after annealing

Abstract

In the paper, we discussed the effect of annealing on the microstructure, crystal texture, and toughness of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) and Ti–4Mo–4Cr–5Al–2Sn–2Zr (TC17) linear friction welding (LFW) joint. The results reveal that the microstructure difference on both welded zone (WZ) decreases. The TC11 WZ consists of supersaturated solid solution α′ phase and β phase, the coarse α grains disappear and the orthorhombic martensite α″ phases transform into lamellar α+α′ phases on the TC17 WZ after the double furnace annealing. Two β textures (shear and annealing textures) and two α textures (D and E textures) exist at the original joint, and both of them transform into new β textures (brass and copper textures) and α textures (F and G textures) after the double furnace annealing. The dislocation density of the TC17 WZ is significantly higher than that of the TC11 WZ at the original joint. After the double furnace annealing, dislocation density, grain type, and Schmid factor (SF) distribute uniformly throughout the entire WZ. The average dislocation density decreases slightly and the low SF (μ<0.25) almost disappears. The microhardness value of the entire joint is more uniform and stable, and the fracture toughness is 137% higher than that of the original joint, approximately reaching 91% of the TC11 fracture toughness. The research provides a theoretical basis for preparing high-toughness joints of dissimilar titanium alloys.