Fatigue Damage of Copper with Ultra-Fine Structure Due to ECAP
Masahiro GOTO, Seung-Zeon HAN, Cha-Yong LIM,@Terutoshi YAKUSHIJI, Tetsushi MORITA and Takaei YAMAMOTO
Abstract:Although there are many studies on the microstructure of various metals with ultra-fine grain formed by ECAP (equal channel angular pressing), a few studies have investigated the fatigue characteristics of ECAPed metals. In the present study, 99.99% pure, oxygen-free copper was used. Before the ECAP process, the material was normalized at 500 for 1 hour. A Bc route with 90rotation after each ECAP cycle was utilized. To obtain the ultra-fine grain with 300nm grain size, a total of 4 passes of ECA pressing with Bc route were performed. Rotating bending fatigue tests of smooth specimens were carried out. Successive observations on the surface damage due to both the direct and the replica observation were carried out to clarify the fatigue mechanism of ECAPed copper. An optical microscope and a scanning electron microscope were used for the observation of the change in surface morphology. A transmission electron microscope was used for observation of microstructure. Putting the experimental results from the observation of each microscope together, fatigue damage of copper with ultra-fine grain was discussed. Key Words:Fatigue damage, ECAP, Copper, Ultra fine grain, Crack initiation, Crack propagation, Grain boundary sliding