2, School of Materials Science and Engineering, University of Science and Technology of China, Shenyang, , China
Fatigue of metals at the nanoscales has drawn extensive attention due to not only the long-term service reliability of nanoscale metallic components in micro/nano-devices, but also the fundamental fatigue mechanisms of the materials at the nanoscales. It has been demonstrated that the decrease in the length scale from micron scales to submicron scales strongly constrains the formation of typical dislocation structures (dislocation walls and cells), and thus suppresses cyclic strain localization, leading to the enhancement of fatigue strength. In this talk, we will present ex-situ TEM investigations on cyclic plasticity and damage behavior of metals at the nanoscales, such as nanocrystalline metal films and metallic multilayers. For nanocryatalline metal films with a thickness ranging from 20 to 930 nm, we found an evident transition of cyclic plasticity from full dislocation-dominated to partial dislocation-controlled behavior, meanwhile grain boundaries exhibit the unstable behavior related to the film thickness. Furthermore, the fatigue damage behavior was characterized, and slip irreversibility was estimated theoretically based on the observations of dislocation activities. For the nanoscale metallic multilayers, we found that the heterogeneous layer interface in the Cu/Ta multilayers with different layer thicknesses exhibits different stability under cyclic loading. The fatigue damage mechanism and the scaling effect on the slip irreversibility, grain boundary as well as heterogeneous layer interface instability of the metal films and multilayers at the nanoscales will be discussed.