Effect of grain boundary segregation on the deformation mechanisms and mechanical properties of nanocrystalline binary aluminum alloys

Abstract

The deformation mechanisms of nanocrystalline (NC) pure Al and NC Al–Co and Al–Mg binary alloys are studied via molecular dynamics simulation. The alloying elements are either segregated to grain boundaries (GB) or distributed randomly as solute. It is revealed that a shear deformation of the pure Al is associated with the GB sliding (GBS) and simultaneous their migration (GBM). GB segregations can significantly alter the mechanisms of plastic deformation. Mg atoms in GBs of the Al–Mg alloy lead to GBS which is accompanied with GBM and a grain growth, while the deformation process of the corresponding alloy with the random distribution of Mg is close to that for pure Al. Unlike Mg, GB segregations of Co atoms detain both GBS and GBM and result in a higher strength of the Al–Co alloy. On the contrary, the strength of the alloy with the Co atoms distributed randomly is very low due to the structure amorphisation leading to the ease of plastic flow. The details of the GBS and GBM processes are further studied for tilt bi-crystals of Al and Al–Co and Al–Mg systems with the alloying atoms being either segregated to the GB or dissolved. It is found that the results for the bi-crystals are in line with those for the NC materials. Overall, GB segregation can strongly influence the response of NC alloys to thermomechanical treatment by affecting such very important mechanisms of plastic deformation in NC metallic materials as GBS and GBM.