Impact toughness and fracture analysis of linear friction welded Ti-6Al-4V alloy joints

Linear friction welding (LFW), as a relatively new solid-state joining technique, has great potentials in welding of non-axisymmetric components, especially for cost-effectively machining blade/disc (blisks) assemblies. In this study, Ti-6Al-4V alloy was jointed by the LFW process under the appropriate processing parameters developed before. The microstructure, impact toughness and fracture characteristics of LFW Ti-6Al-4V joint were investigated. The results showed that a sound weld was obtained consisting of a superfine α + β microstructure in the weld center (about 70 μm thickness). The weld presents a higher impact toughness (61.3 ± 5.8 J/cm²) than the parent Ti-6Al-4V because of the superfine microstructure formed in the weld. The fracture surface exhibits three typical regions: the thin fibrous zone close to the notch, the radiation zone in the middle and the shear lip zone at the other three sides, corresponding to the crack initiation, propagation and shear failure zones, respectively. The crack develops a short distance along the weld center and thermomechanically affected zone after its initiation, and then extends into the parent metal due to the lowest impact toughness of the parent.