Cyclic deformation behavior of double-slip-oriented copper single crystals IV: change of hysteresis loop shape and formation of persistent slip bands

The changes of hysteresis loop shape parameter VH with number of cycles N in copper single crystals oriented for conjugate, critical and coplanar double slip were detected systematically during cyclic deformation. The results of multiple slip-oriented copper single crystals [001], [1̄11] and [011] were also included for summary. It was shown that, unlike the result obtained for single slip crystals, the crystallographic orientation has a strong effect on the trend of hysteresis loop shape change during cycling for double slip-oriented crystals. The persistent slip bands (PSBs) may occur at certain strain amplitudes within or even below the plateau region in the cyclic stress–strain (CSS) curve for [1̄12] crystals, while it is very hard for PSBs to form in [2̄33] and [017] crystals. In brief, whether VH could be adopted to determine the PSB nucleation stress is closely related to the existence or non-existence of a plateau or quasi-plateau region in the CSS curves of the crystals with various orientations. The PSB nucleation stresses determined by the parameter VH for copper single crystals with different types of double slip orientations were compared and discussed.