Linear friction welding of equiaxed Ti17 titanium alloy: Effects of microstructure evolution on tensile and impact properties

Linear friction welding of equiaxed Ti17 titanium alloy with great strength–plasticity matching was carried out in this study and the microstructure evolution, tensile property and impact toughness of this joint were investigated in detail. Results show that α dissolution (α → metastable β transformation) takes place in both thermo-mechanically affected zone (TMAZ) and weld zone (WZ). The metastable β in TMAZ near base metal (BM) is affected by stress during welding, resulting in concentrated orientation and high dislocation density. Dynamic recrystallizations of α and metastable β phases occur in TMAZ near WZ, leading to fine recrystallized α grains and equiaxed recrystallized β grains. Complete α dissolution and total dynamic recrystallization appear in WZ owing to the effect of strong thermomechanical coupling. Above microstructure evolution causes significant work hardening and fine grain strengthening effects, counteracting the weakening effect induced by α dissolution, and resulting in the tensile strength (1250.0 MPa), elongation (12.2%) and impact toughness (28.8 J/cm²) of the joint are higher than those of the BM. In addition, the tensile strength and elongation of the equiaxed Ti17 joint are increased compared to those of bimodal as well as basketweave Ti17 joints.