粗晶纯铝疲劳位错结构的热稳定性

Thermal stability of fatigue dislocation structures in coarse-grained pure aluminum

在不同总应变幅下对高层错能粗晶纯铝进行疲劳实验直至达到近似相同的累积应变量,然后再在不同温度(200、330和450℃进行退火处理。利用透射电子显微镜观察疲劳位错结构及其退火后微观结构的变化。结果表明:粗晶纯铝疲劳位错结构主要为胞结构,胞尺寸随着外加应变幅的升高逐渐减小,胞壁逐渐变得致密,胞内位错密度下降;粗晶纯铝疲劳处理后在3个温度下进行退火处理,所有样品的疲劳位错结构均发生明显的回复现象;只是在相对较低温度200℃退火时,低应变幅下形成的位错结构的回复机制主要为空位消失和异号位错相消,而中、高应变幅下位错结构的回复机制主要表现为多边形化回复机制。粗晶纯铝经不同总应变幅疲劳后的DSC曲线测量结果与TEM观察结果基本一致。

Coarse-grained pure Al with a high stacking fault energy was first fatigued at different total strain amplitudes (?εt/2) up to almost the same accumulated strain, and then annealed at different temperatures (200, 330 and 450 ℃) for 30 min. The fatigue dislocation structures as well as the microstructural changes resulting from subsequent annealing treatments were detected by TEM. The results show that the dislocation structures of fatigued pure Al are mainly characterized by dislocation cells. With increasing ?εt/2, the average cell size decreases, the cell walls become more densified, and the density of dislocations in cells decreases. For the coarse-grained pure Al samples fatigued and then annealed at those three temperatures for 30 min, a clear recovery of fatigue dislocation structures occurs for all samples. The only difference exists in the recovery mechanism of the samples fatigued at different strain amplitudes and then annealed at a comparatively lower temperature of 200 ℃; for instance, the recovery process of dislocation structures induced by fatigue at lower strain amplitude is mainly determined by the disappearance of vacancies and the annihilation of dislocations of opposite sign, while the polygonization recovery dominates at higher strain amplitudes. The results of DSC measurements on the pure Al samples fatigued at different strain amplitudes are basically consistent with the results of TEM observations.