Wear-induced microstructural evolution of nanocrystalline aluminum and the role of zirconium dopants

Abstract

Wear and friction of nanocrystalline (NC) aluminum were investigated via molecular dynamics simulations and the effects of dopants were considered. Zr-doped NC Al was found to have a better wear resistance and a smaller friction force, which is consistent with a higher hardness and a higher strength of the doped sample. The underlying mechanisms are suppressed emission of dislocations from grain boundaries (GBs), suppressed GB migration, and suppressed GB sliding. After multiple sliding cycles, the trend in mechanical response was reversed, with the pure NC Al showing a better wear resistance and a lower friction force than the doped sample. One reason is that the higher dislocation density introduced during wear into the pure sample leads to more strain hardening. Another reason is that the pure NC Al has undergone more significant grain growth than the doped sample. Since the grain size of our samples is in the inverse Hall-Petch regime, here grain growth leads to strengthening of the pure sample. Mechanisms of grain growth in the pure NC Al and its suppression in the doped NC Al are analyzed and discussed.