Abstract:Ultrafine-grained (UFG) pure titanium was produced by equal channel angular pressing for 4 passes, followed by rotatory swaging at room temperature. The strain-controlled low-cycle fatigue tests of UFG and coarse-grained (CG) pure titanium were conducted by Instron electro-hydraulic servo fatigue testing machine in the strain amplitude range of 0.5%–1.1% at room temperature. Transmission electron microscope (TEM) and scanning electron microscope were used to investigate the microstructure and fracture surface of UFG pure titanium after fatigue tests. Results show that UFG pure titanium exhibits a longer low-cycle fatigue life, compared with the CG pure titanium. For example, at a total strain amplitude of 0.5%, UFG and CG pure titanium has fatigue life of 10 850 and 4820 cycles, respectively. Significant cyclic softening occurs in UFG pure titanium, except in the case of a total strain amplitude of 0.5%. Hysteresis loop area is increased rapidly with the increase in strain amplitude. The fracture surface shows that the fatigue crack is initiated from the specimen surface. A series of fatigue striations and many microcracks exist in the propagation region. With the increase in strain amplitude, the predominant failure mode is transformed from ductile failure into quasi-cleavage failure. Dislocation slip is the main plastic deformation mechanism of UFG pure titanium during low-cycle fatigue deformation.