The environment (air, water, solution, electrolyte) can have a profound impact on deformation processes for light-weight metals (Al, Mg, Ta, Li …) that have a high affinity to oxygen. Similar impacts of the environment are seen for electrode materials. One can further imagine that as the characteristic size of these materials shrinks, surface reactions will contribute more and more, likely changing substantially the mechanical properties of the nano-device. By developing a reactive molecular dynamics method, we demonstrated how oxidation changes the deformation and failure mechanism in a nano-scale device, for example in an Al nano-wire. The nano-scale mechanisms also have a profound impact in large scale manufacturing processing, such as the tribology and surface quality of Al sheets for car panels made with hot forming processes.
This figure shows during hot-forming of Al-Mg alloy to make the lift gate of a car, nanowires were formed at adhered interfaces. Reactive molecular dynamics shows that Al nanowire deformation is drastically different in vacuum and O2. Nature Communication (2014).
We are further addressing environmental effects for a variety of problems. For example:
- How Mg fractures differently in air and vacuum?
- Why nano-crystalline Al2O3 appears to be superplastic when oxygen diffuses into the grain boundaries?
- Under what conditions do diamond-like carbon films become almost frictionless in a H2 or H2O environment?
- How to ensure an always-passivated surface?
- “Oxidation-assisted ductility in aluminum nanowires”, F.G. Sen, A.T. Alpas, A.C.T. Van Duin, Y. Qi, Nature Communications (2014)
- “Oxidation induced softening in Al nanowires”, F.G. Sen, Y. Qi, A.C.T. Van Duin, A.T. Alpas, Appl. Phys. Lett. 102, 05192 (2013)
- “Environmental conditions to achieve low adhesion and low friction on diamond surfaces”, H. Guo and Y. Qi, Mod. Sim. Mat. Sci. Eng. 18, 034008 (2010), Focus issue on contact and friction modeling (Invited Article)
Shutian Yan (ME student co-advised by Dr. Sharon Xiao)