Temperature-dependent residual broadening of x-ray diffraction spectra in nanocrystalline plasticity

In situ x-ray diffraction peak profile analysis at room temperature has shown that peak broadening during plastic deformation is reversible upon unloading for nanocrystalline metals, demonstrating the lack of a developing permanent dislocation network. In this letter, we show that the peak broadening is not reversible when similar load-unload cycles are performed at 180 K. However, by then warming the sample to 300 K, peak broadening recovers to a great extent and all subsequent plastic deformation load∕unload cycles are characterized again by a reversible peak broadening. The temperature-dependent residual peak broadening provides explicit evidence of a thermal component in the nanocrystalline deformation mechanism.