Microstructural stability during cyclic loading of multilayer copper/copper samples with nanoscale twinning

The response to cyclic deformation has been studied for Cu/Cu multilayer material consisting of columns of closely spaced, parallel nanotwins. The fatigue life under stress-controlled cycling is greatly improved over that of coarse-grained Cu. Nanotwinning provides significant strengthening, which is unchanged by fatigue or severe compression. Observations by focused ion beam microscopy showed that the microstructure is quite stable under deformation. Localized deformation from indentation produced shear bands and apparently some loss of nanotwinned area but no decrease in hardness.