材料期刊网

通过差示扫描量热仪(DSC)和显微硬度测试研究了等通道转角挤压(ECAP)制备的超细晶铜在退火条件下的热稳定性和硬度变化, 同时利用扫描电镜电子通道衬度(SEM--ECC)技术和透射电镜(TEM)研究了超细晶铜在室温到300 ℃的温度范围内分别在单向压缩和循环变形后的微观结构变化. 结果表明: 超细晶铜即使在低于再结晶温度退火条件下也会以缓慢渐进的方式发生逐步的再结晶和晶粒粗化, 该结构软化过程通过DSC随退火时间的响应曲线探测不到. 高温压缩下晶粒的粗化行为与应变速率有关, 应变速率越大, 粗化的局部化越明显; 应变速率越小, 更多的晶粒发生整体粗化. 高温循环加载促使晶粒粗化发生得更为显著、均匀, 在粗化的晶粒内可观察到一些典型的位错组态, 如墙结构和胞结构等. 另外, 利用最大晶粒尺度(D_max)与平均晶粒尺度(D_aver)的比值V定量讨论了不同高温变形情况下晶粒粗化的不均匀性.

The thermal stability and hardness behavior of ultrafine--grained (UFG) copper produced by equal channel angular pressing (ECAP) under the condition of annealing were studied by differential scanning calorimeter (DSC) and micro--hardness tests, and the microstructural changes of this material under uniaxial compression or cyclic deformation at temperatures ranging from room temperature to 300 ℃ were examined by electron channeling contrast (ECC) technique in scanning electron microscopy (SEM) and by transmission electron microscopy (TEM). It was found that under annealing even at a certain temperature below recrystallization temperature, UFG copper would exhibit a structural evolution, i.e., recrystallization and grain coarsening, the process of which may happen gradually at a low developing rate, so that the DSC response curve as a functional of annealing time cannot detect such a process. The grain coarsening behavior of UFG copper under high--temperature compression is related to the strain rate, i.e., the higher the strain rate, more remarkable the localization of grain coarsening becomes; the lower the strain rate, many more grains become coarsened integrally. Comparatively speaking, the grain coarsening induced by high--temperature cyclic deformation takes place more notably and uniformly, and some typical dislocation arrangements, like dislocation walls and dislocation cells etc., can be observed in some coarsened grains. Also, the inhomogeneity of grain coarsening under high--temperature deformation was quantitatively discussed in terms of a ratio V of maximum grain size (D_max) to average grain size (D_aver), which is available for the coarsened grains.