Abstract:Ultrafine grained (UFG) commercially pure Zr was prepared by Equal Channel Angular Pressing (ECAP) and Rotary swaging (RS). The Low cycle fatigue properties of the UFG pure Zr were investigated by a method under axial loading controlled by symmetric strain. The characteristics of cyclic stress and strain response and hysteresis loop of UFG pure Zr were discussed. Softing and hardening characteristics and cumulative hysteresis of the UFG pure Zr were analyzed and then the fatigue life was predicted. The results indicate that the cyclic softening and hardening properties of UFG pure Zr depend on the size of the applied total strain amplitude, and the softening ratio is most significant when the total strain amplitude is more than 1.0%. The hysteresis loop area increases with the total strain amplitude increasing, and the “ratchet phenomenon” occurs when the strain amplitude is small. Regression analysis shows that the fatigue life of UFG pure Zr matches Coffin-Manson"s empirical