Shear bands in cyclically deformed ultrafine grained copper processed by ECAP

Surface Deformation Features in Ultrafine-Grained Copper Cyclically Stressed at Different Temperatures

“…1(a), which were also often reported in other previous * Corresponding author, E-mail: xwli@mat.eng.osaka-u.ac.jp or xwli6988@hotmail.com work. 5,8,9,12,13,16) Two sets of SBs, which are roughly perpendicular to each other, were clearly observed to appear on the maximum resolved shear stress plane making approximately 45 with the loading axis. Observations also revealed that some SBs extended across the entire surface of sample, although the initial grain size is just some hundred nano-meters.…”

“…It has been commonly recognized that room-temperature fatigue damage in UFG materials is basically attributed to the formation of shear bands, which can extend over far larger scales than the initial grain size. 5,6,8,9,12,13) However, the cyclic deformation features and damage behaviour of such UFG materials at temperatures above room temperature has never been reported so far. Quite recently, we have tentatively studied the fatigue behaviour and microstructures of ECA-pressed copper at temperatures between room temperature and 573 K under a constant stress amplitude of 200 MPa.…”

Stress‐Amplitude‐Dependent Deformation Characteristics and Microstructures of Cyclically Stressed Ultrafine‐Grained Copper

“…Several investigators have given some explanations on the formation of SBs in deformed UFG copper, [21,22,25,26,30,[40][41][42][43][44][45][46] and some disputable opinions have arisen. For examples, Mughrabi and Höppel [21] suggested that the formation of SBs might be related with local grain/ subgrain coarsening during cycling, whereas Wu et al [25,26] reported that no detectable grain coarsening was observed in the vicinity of SBs, and they held that the formation of SBs may be attributed to both oriented distribution of defects along shear plane of last pressing and local reversible and irreversible deformation.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Apparently, the understanding of the fatigue properties (among various mechanical properties) of such UFG materials is of particular importance for their practical engineering applications, many investigators have thus been attempting to explore the fatigue deformation mechanisms of UFG materials, especially of UFG copper, with different emphases. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] It is now commonly recognized that the low-cycle fatigue damage in UFG materials primarily results from the formation of shear bands (SBs), which can extend over far larger scales than the initial grain size, [18][19][20][21][22][23][24][25][26] and that the cyclic softening phenomenon as well as the deterioration in fatigue life under strain-amplitude-controlled tests in the low-cycle fatigue (LCF) regime is attributed to grain coarsening due to instabilities of the ECAPed structures during cycling. …”

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

“…In particular, the following characteristic features in cyclic deformation of UFG Cu processed by ECAP have been sporadically reported: (1) cyclic softening is frequently detected as a stress-strain response, [9][10][11][12][13] (2) macroscopic shear bands (SBs) are formed inhomogeneously, 9,10,13-18) (3) coarse grains are locally developed. 9,12,14,15,[19][20][21] For example, Wu et al 14,15) observed no grain coarsening, while they found apparent SBs by scanning electron microscopy (SEM) observation. Therefore, they concluded that there is no relationship between the SB formation and the grain coarsening.…”