Connecting Oxide Bifilms’ Properties from Atomistic Simulations with Virtual Casting of Aluminum
Aluminum oxide bifilms, formed during melt turbulence flow, can have a significant detrimental effect on material properties after they are entrapped in the final cast products. Recently, molecular dynamics (MD) simulations were used to simulate the formation and fracture mechanisms of bifilms at the nano-scale, which are hard to obtain experimentally. The results showed that the fracture occurred at the Al/oxide interface instead of the oxide/oxide interface for both amorphous oxide and crystalline α-Al2O3, which represent the “young” and “old” oxides referred in aluminum casting. The fracture energy is higher for the α-Al2O3 bifilm. However, if OH-termination contamination occurs due to residue hydrogen gas and water trapped in the aluminum oxide bifilm interface, the OH-termination oxide bifilm fractured at the oxide/oxide interface and with a much-reduced fracture energy. This is consistent with the general picture that oxide bifilms will initiate cracks, especially fatigue cracks in cast aluminum products. For macroscopic models, crack initiation and propagation can be modeled by cohesive zone method. Therefore, we propose a simple size bridging relationship to connect the MD-predicted oxide bifilms fracture energy and fracture strength with future finite element modeling.
KeywordsOxide bifilms Molecular dynamics Interfaces Aluminum alloys Castings
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