UC Irvine

The bimodal structure has become a promising way to alleviate the famous strength and ductility trade-off in metals. For conventional nanocrystalline metals, strong strength softening follows after the Hall-Petch effect within the continuous decrease of grain size. In our study, we conducted molecular dynamics (MD) study and discovered that as the decrease of small grain size in bimodal nano-grained structures, the softening rate of the inverse Hall-Petch effect is suppressed. With the increasing number of small grains around the large grains, the plasticity of large grains is enhanced, and they also undergo less intergranular grain boundary sliding and migration leading to the increasing stress of large grains. The discovery of this process could be beneficial to designing bimodal nano-grained structures with desired ductility and strength.