纯度对ECAP制备超细晶铜疲劳性能的影响

EFFECT OF PURITY ON FATIGUE PROPERTIES OF ULTRAFINE GRAINED CU PROCESSED BY EQUAL CHANNEL ANGULAR PRESSING

摘要:

等径弯曲通道挤压(ECAP)制备超细晶材料因具有优异的机械性能而备受关注,其疲劳性能是获得广泛应用的关键。本文采用应力比R = -1的对称加载疲劳试验,研究了ECAP制备超细晶高纯铜(LP Cu)、低纯铜(HP Cu)的疲劳行为,分析了循环应力-应变响应、疲劳寿命和疲劳前后晶粒取向分布,讨论了纯度与超细晶材料疲劳稳定性的关系。结果表明：在任何应力幅下,获得的超细晶低纯铜的寿命都大于ECAP变形前的粗晶铜,在相同应力幅下,循环周次约提高到1.6~2.0倍。而超细晶高纯铜的疲劳曲线,表现出不同的特性,在高应力幅下,超细晶高纯铜具有较高的疲劳寿命,但在低应力幅下,超细晶高纯铜循环周次下降,疲劳寿命低。在应力控制条件下,随应力幅的降低,超细晶纯铜的循环应力-应变响应从循环软化逐渐过渡为循环硬化。杂质的存在能有效阻止疲劳过程晶粒的转动和位错的运动,降低其回复软化,减小相邻晶粒间取向差变化,使超细晶低纯铜与超细晶高纯铜相比有较大的循环硬化指数n和循环硬化系数K,具有较好的疲劳稳定性。

Abstract:

The ultra-fine grain(UFG) material by Equal Channel Angular Pressing (ECAP) has attracted attention for excellent mechanical performance. The fatigue properties of UFG by ECAPSareScriticalSto wide application. The fatigue properties of ultra-fine grain high purity(HP) and low purity(LP) copper by ECAP were investigated by fatigue tests conducted in air, at symmetrical loading ratio R= -1. The cyclic stress-strain response, fatigue life and grain orientation distribution before and after fatigue were analyzed. The relationship between purity and fatigue stability of ultra-fine grain copper were discussed. The results showed that the stress-controlled fatigue life of UFG low purity copper is longer about 1.6~2.0 times than that of their coarse grain (CG) counterparts under any stress amplitude. On the other hand, the fatigue curve of UFG high purity copper shows different characteristics. TheSfatigueScyclesSto failure of UFG Hp copper is strongly dependent upon the applied stress amplitude and decrease sharply withSstress amplitude decreasing. Under lower cyclic stresses, UFG Hp copper exhibitsSlower fatigue lives. Cyclic stress-strain response of UFG Cu under stress-controlled loading change from cyclic softening to cyclic hardening with stress amplitude decreasing. The UFG low purity copper shows a relatively high cyclic strain hardening exponent, hardeningShardeningScoefficient and fatigue stability with respect to the UFG high purity copper, because the impurity hinder grain rotation and dislocation motion, decline recovery rate, and reduce grain orientation modifies.