On Corrosion and Stress Corrosion Cracking Behavior of Nanocrystals

对采用等通道转角挤压(ECAE)技术制备的超细晶(UFG)铜(平均晶粒度为200 nm)和常规铜试件进行了恒定电位下的应力腐蚀试验。UFG铜表面呈现出典型的整体腐蚀特征。然而，与普通铜相比，超细铜具有很高的耐腐蚀性(平均晶粒度为20μ)。经过严重塑性变形(SPD)，晶格位错全部流向晶界，在超细晶铜晶界形成了极高的位错密度。位错密度越高，超细晶铜晶界的腐蚀电位越高。另一方面，由于晶粒内部产生了很强的应变场，腐蚀电位也随之升高。溶解受晶界和晶内电位差的控制，UFG铜的应力腐蚀敏感性比普通铜和相同晶粒度的退火态UFG铜要低。在室温下的测试中观察到了增益边界滑移。这种GBS在UFG铜的SCC行为上起到了应力释放部位的作用。

Corrosion tests under a constant potential, stress corrosion cracking (SCC) tests were performed on the ultra fine grained (UFG) copper (avarage grain size : 200 nm) manufactured by Equi-Channel Angular Extrusion (ECAE) technique and on conventional copper specimens. The surface of the UFG copper showed a typical general corrosion. However, the UFG copper has a very high corrosion resistance compared with the conventinal copper (average grain size : 20μ). By Severe Plastic Deformation (SPD), all lattice dislocations flowed out to the grain boundary, so the extremely high dislocation density was formed at the grain boundary of UFG copper. The corrosion potential at the grain boundary of UFG copper was increased by the high dislocation density. On the otherhand, a very strong strain field was induced in the grain interior, so the corrosion potential became high, too. Disolution is controlled by the difference of potential between grain boundary and grain interior.The susseptibility to stress corrosion cracking of UFG copper was very low compared with conventinal copper and annealed UFG(the same grain size). The gain boundary slidings (GBS) were observed during the tests at room temperature. This GBS acts as a stress relieving sites on the SCC behavior of the UFG copper.