Deformation of Al nanowires in an oxygen environment
Fatih Sen (University of Windsor), Yue Qi (General Motors R&D), Adri van Duin (Pennsylvania State University), Ahmet Alpas (University of Windsor)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium B
Tue 4:20 - 5:40
CIT 227
Few materials deform in vacuum. For nano-structured materials, as the surface to volume ratio increases dramatically, the surface reactions occurring in enviroment can significantly alter the deformation mechanisms. To couple chemistry and mechanics, we used molecular dynamics (MD) simulations in conjunction with reactive force field (ReaxFF) to simulate the deformation process of single crystal Al nanowires (NW) in an oxygen environment. In O2, an amorphous oxide shell with a thickness of ~1 nm formed on the Al NWs with 3.2-5.6 nm radii. We found the surface oxidation changed the modulus, yield stress, and the fracture process of an Al nanowire. As shown before pure Al NWs yielded by nucleation of partial dislocations from the surface, and did not show significant ductility in vacuum. However, when the Al NW was covered with an oxide, the dislocation nucleation from the Al/oxide interface occurred at a lower stress. The native oxide on the Al NW was revealed to be softer and also more ductile than the single crystal Al due to its low density and oxygen deficient structure. In O2, when the strain rate is slow enough, the oxide shell showed interesting superplastic deformation behaviour due to continuous surface oxidation that repaired the broken Al-O bonds.