Orientation Design for Enhancing Deformation Twinning in Cu Single Crystal Subjected to Equal Channel Angular Pressing

Abstract

Slip and twinning are two major mechanisms in plastic deformation of crystalline materials; however, twinning is extremely difficult to occur in face‐centered‐cubic crystals under conventional conditions. The authors show that twinning becomes an active deformation mode in copper single crystal when subjected to equal channel angular pressing at room temperature. In particular, the observations revealed that deformation twinning became more active in the copper single crystal having a proper crystallographic orientation.

Origin of deformation twinning from grain boundary in copper

“…The crystallographic orientation of the Cu single crystal was specially designed to make one of twinning systems, such as ͑111͓͒112͔, just on the macroscopic shear deformation plane of ECAP, which has been described in more detail previously. 26 Some of deformation twins nucleated in the very fine ribbon structures in the region of shear bands, and most of them are in a scale of tens of nanometers except for few of them with a length larger than 100 nm, as reported in more detail elsewhere. 26 After ECAP, thin foils for transmission electron microscope ͑TEM͒ were prepared by twin-jet polishing method.…”

“…25,26 Such crystallographic design of the single crystal will greatly activate deformation twinning. The crystallographic orientation of the Cu single crystal was specially designed to make one of twinning systems, such as ͑111͓͒112͔, just on the macroscopic shear deformation plane of ECAP, which has been described in more detail previously.…”

“…25,26 Such crystallographic design of the single crystal will greatly activate deformation twinning. 26 Figure 1͑a͒ is a typical bright-field TEM image showing a group of twins nucleated in a slightly larger ribbon structure in the region of shear band. High-resolution TEM ͑HRTEM͒ and TEM were performed on a 300 kV Tecnai G 2 F30 and a 200 kV JEM-2000FXII, respectively.…”

“…tion except for the difference in the length scale. 24,26 Also a special orientation was selected, which promotes deformation twinning easily. Figure 2͑a͒ presents a typical HRTEM image of a deformation twin nucleated at the GB and stopped in the interior of grain with a tower shape.…”

Investigation of texture and mechanical properties of copper processed by new route of equal channel angular pressing

“…Copper has a moderate value of stacking fault energy ($80 mJ m À2 ) [20]. Han et al [24] and Han et al [25] showed that Cu single crystal can be deformed by twinning under the conditions of very low strain rate and room temperature during ECAP provided an appropriate crystallographic orientation was selected with respect to the ECAP die. This mech- anism can also lead to grain refinement of copper during ECAP process.…”