ECAP+旋锻变形制备超细晶纯锆的低周疲劳行为

Low Cycle Fatigue Behavior of Ultrafine Grained CP-Zr Processed by ECAP and RS

采用等径弯曲通道(ECAP)+旋锻(RS)复合变形技术制备了超细晶工业纯锆,通过轴向对称应变控制方法对超细晶纯锆的低周疲劳性能进行研究,讨论了超细晶纯锆的循环应力-应变响应、软硬化特性、累积滞后规律、疲劳寿命及其疲劳断裂机理。结果表明:超细晶纯锆的循环软硬化特性依赖于外加总应变幅的大小。随应变幅的增加软化速率逐渐增大,且当总应变幅大于1.0%时,材料完全呈现循环软化特性。滞后回线面积随着总应变幅的增大而增大,当应变幅较小时出现"棘齿现象"。回归分析表明超细晶纯锆疲劳寿命满足Coffin-Manson经验关系式。超细晶工业纯锆低周疲劳的疲劳机制为位错运动,其断裂类型为韧性断裂。

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 relationship. The fatigue mechanism of low cycle fatigue of UFG pure Zr is dislocation motion, and the fracture type is ductile facture.