Low cycle fatigue properties of linear friction welded joint of TC11 and TC17 titanium alloys

Abstract

In this works, we investigated the microstructures and low cycle fatigue (LCF) performance of linear friction welded (LFWed) joint of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) and Ti-4Mo-4Cr-5Al-2Sn-2Zr (TC17) titanium alloys. The results show a large number of fine lath martensite precipitations α′ with three variants occur on the welded zone (WZ) of TC11 side, and coarsened β phases with a small amount of precipitations appear on the WZ of TC17 side. The orientation relationship of matrix and precipitation is 〈112¯0〉p//〈111〉m and {0001}p//{110}m. The stress amplitudes and plastic strain amplitudes exhibit cyclic softening characteristics at higher total strain amplitudes (0.8–1.2%) for the damaging dislocation tangles and obstacles with cyclic deformation process. The increasing rate of softening with the increasing strain amplitudes is due to more slip systems starting and complete shearing of martensites. Elastic moduli of the joint during the loading and unloading phases are constant at lower total strain amplitudes, which decrease with increasing strain amplitudes and increasing number of cycles at the higher total strain amplitudes. Meanwhile, as the applied total strain amplitude decreases, the number of cycles to failure increases, and the fatigue lifetime follows the Basquin's equation and Coffin–Manson relationships. Finally, the fragment of the joint locates at the WZ of TC17 side and propagates along the flow direction of plasticized materials.