Effect of grain size on the competition between twinning and detwinning in nanocrystalline metals

Both twinning and detwinning have been reported to occur during the deformation of nanocrystalline (nc) face-centered-cubic metals. This raises the issue of how these two processes compete with each other. Here, we report that the twinning process dominates in a certain range of grain sizes, whereas, the detwinning process dominates outside of this range to annihilate all twins. These experimental observations establish a full spectrum of grain-size effects on deformation twinning and detwinning and are explained by the deformation physics. They also provide a fundamental basis for understanding and designing the mechanical behavior of nc metals and alloys.