Cyclic deformation behavior of linear friction welded Ti6Al4V joints

This study was aimed at characterizing microstructural change and fatigue properties of linear friction welded (LFWed) Ti6Al4V joints with special attention to the relationship between the microstructure and cyclic deformation behavior. The welding process resulted in a remarkable microstructure change across the LFWed joint. The microstructure of the joint consisted of fine subgrains in the weld zone (WZ) and elongated grains in the thermomechanically affected zone (TMAZ), leading to a significantly higher hardness in the WZ. Both the base metal (BM) and joint exhibited essentially symmetrical hysteresis loops and equivalent fatigue life, while the cyclic strain hardening exponent of the welded joint was lower. Cyclic stabilization appeared at lower strain amplitudes up to 0.6% in both the BM and joint, however, cyclic softening occurred at higher strain amplitudes. Fatigue failure was observed to occur in the BM, and fatigue crack initiated from the specimen surface or near-surface defect. Fatigue crack propagation was basically characterized by fatigue striations, together with some secondary cracks.