共轭和临界双滑移取向Cu单晶体疲劳位错结构的热稳定性研究

INVESTIGATIONS ON THERMAL STABILITY OF FATIGUE DISLOCATION STRUCTURES IN CONJUGATE AND CRITICAL DOUBLE-SLIPORIENTED Cu SINGLE CRYSTALS

在不同塑性应变幅下对[2ˉ23]共轭双滑移和[017]临界双滑移取向Cu单晶体进行疲劳实验直至循环饱和,然后在不同温度下进行退火处理,考察了其位错结构的热稳定性.结果表明,300℃退火处理后,位错结构发生了明显的回复;500和800℃退火处理后,均发生了明显的再结晶现象,并伴随退火孪晶的形成.不同取向Cu单晶体循环变形后形成不同的位错结构,其热稳定性由高到低依次为:脉络结构、驻留滑移带(PSB)结构、迷宫或胞结构.不同取向疲劳变形Cu单晶体中形成的退火孪晶均沿着疲劳后开动的滑移面方向发展,疲劳后的滑移变形程度越高,退火后形成的孪晶数量则越多.但过高的退火温度(如800℃)会加快再结晶晶界的迁移速率,进而抑制孪晶的形成,致使孪晶数量有所减少.

It is well known that the cyclic deformation behavior and dislocation structures of Cu single crystals with different orientations have been systematically investigated and understood.However,there is as yet no general and unequivocal knowledge of the thermal stability of fatigue-induced dislocation structures in Cu single crystals,which is particularly significant for the further improvement of low energy dislocation structure（LEDS）theory.In previous work,the thermal stability of fatigue dislocation structures in [4ˉ 18 41] single-slip and [2ˉ33]coplanar double-slip Cu single crystals have been reported.For deeply understanding the orientation-dependent thermal stability of fatigue dislocation structures,in the present work,[2ˉ23] conjugate and [017] critical doubleslip-oriented Cu single crystals were cyclically deformed at different plastic strain amplitudes gplup to saturation,and then annealed at different temperatures（300,500 and 800 ℃） for 30 min,to examine the thermal stability of various fatigue-induced dislocation structures.It was found that an obvious recovery has occurred in various dislocation structures at 300 ℃.At the higher temperatures,e.g.,500 and 800 ℃,a remarkable recrystallization phenomenon takes place together with the formation of many annealing twins.The thermal stability of various dislocation structures produced in fatigued Cu single crystals with different orientations from high to low are on the order of vein structure,persistent slip band（PSB） structure,labyrinth structure and dislocation cells.The annealing twins formed in Cu single crystals with different orientations all develop strictly along the dislocation slip planes,which have been operated under fatigue deformation.The more serious the fatigue-induced slip deformation,the greater the amount of annealing twins would be.Furthermore,an over high annealing temperature,e.g.800 ℃,would greatly speed up the migration of boundaries of recrystallized grains to restrain the formation of annealing twins,leading to,more or less,the decrease in the amount of twins.