Study on the application of ultrafine grained copper to electric materials.

本文通过对ECAP处理后的超细晶铜进行疲劳试验，研究了其疲劳机理。通过试验分析，阐明了疲劳裂纹的萌生行为、表面硬度变化与应力疲劳损伤的关系、裂纹扩展行为和扩展机理以及控制光滑试件疲劳寿命的表面小裂纹扩展规律。此外，由于非平衡晶界导致的组织不稳定性导致了长寿命区疲劳强度的提高，因此采用ECAP后退火的方法提高了长寿命区的疲劳强度。铜（99.9%Cu）在180℃下进行ECAP后退火的结果表明，在2 × 10^7次循环下的疲劳强度提高（约为具有99.99%Cu的ECAP处理后的铜的1.4倍）。

In the present study, the fatigue tests of UFG copper processed by ECAP were conducted to clarify the fatigue mechanism. The experimental analysis was made and the fatigue crack initiation behavior, the relationship between the change in surface hardness and fatigue damage due to stressing, the crack growth behavior and growth mechanism, and the growth law of small surface-cracks which control the fatigue life of smooth specimens, were clarified. In addition, post-ECAP annealing was conducted to improve the fatigue strength in a long-life field because that the less improvement of fatigue strength in long life fields resulted from instability of microstructure with non-equilibrium grain boundaries. Results of copper (99.9%Cu) with post-ECAP annealing at 180℃ showed the enhanced fatigue strength at 2x10^7 cycles (about 1.4 times of as-ECAPed copper with 99.99%Cu).