Fatigue behavior and damage characteristic of ultra-fine grain low-purity copper processed by equal-channel angular pressing (ECAP)

Cyclic Deformation Behavior of Ultra-Fine Grained Copper Produced by Equal Channel Angular Pressing

“…In the previous studies mentioned above, 13,14,17,18,27) it has been concluded that there is no relationship between the SB formation and the grain coarsening since as-ECAPed grain structures are kept in fatigued specimens with clear SBs. On the contrary, Mughrabi and Höppel, 19) and Höppel et al 20,28) have insisted that the grain coarsening plays a dominant role in the formation of the SBs.…”

“…These structural features of the SBs characterized by the present study are consistent with those reported in the literature. 9,11,14,16,18) Changes in grain size and grain morphology of the fatigued specimens were observed using the EBSD method. Grain maps obtained from an as-ECAPed material and a specimen Fig.…”

“…5(b) that the other major grains slightly grow up to 1-2 mm and elongate into the same direction as that observed in the coarse grains. Although Wu et al, 14) Kunz et al, 13) Lukáš et al 17,27) and Xu et al 18) conducted SEM observations in fatigued commercial-purity UFG Cu (99.8%-99.9%) produced by ECAP, they all concluded that no detectable grain coarsening took place during cyclic deformation. This result is obviously in disagreement with the present result.…”

“…These findings inevitably raise the question of whether the development of the SBs is related to the cyclic softening. Xu et al 18) and Kunz et al 13) have concluded that there is not a one-to-one correlation between the SB formation and the cyclic softening since they both have found distinct SBs even in the case of cyclic hardening. Moreover, they could provide no microstructural evidence of the cyclic softening.…”

Evaluation of crack growth rate and growth model of ultrafine grained copper

“…It should be concluded that, thus, the initial (moderate) drop in hardness appears to result mainly from a decrease in the dislocation density inside the grains/GB-regions and the formation of SBs. Regarding the dislocation density after fatigue, Xu et al [15] conducted strain-controlled fatigue tests of commercial copper (99.8% Cu) processed by ECAP for 6 passes through C-route (after each pressing, the billet bar was rotated around its longitudinal axis through 180˚). From TEM observations and EBSD grain maps, they indicated that post-fatigued structures have narrower GBs and lower dislocation density in grain interiors when compared to those in virgin microstructures.…”