The corrosion resistance of metals relies on a passivating surface layer of dense and adherent oxide. In gas turbines, nuclear plants, humid environments, or even solar sails, hydrogen-induced interfacial failure, such as blistering at the metal/oxide interface and oxide film spallation, can be severe. As a result, the integrity of such a protective oxide is often compromised in the presence of excess hydrogen. However, existing theories fail to explain how a nanoscale gas bubble manages to reach its critical size at the metal/oxide interface before the oxide layer can deform.
Inspired by our most recent works and after more than two year’s hard work, for the first time, we proposed and revealed with solid experimental evidence that “pre-blister cavitation” formed through surface diffusion inside the metal is the core of this age old riddle. Using in situ environmental transmission electron microscopy, we have discovered that once the aluminum metal/oxide interface is weakened by the segregating hydrogen, rampant surface-diffusion of Al atoms sets in to form numerous gas-accumulating cavities on the metal side driven by Wulff reconstruction. The morphology and growth of these metal-side cavities are found to be highly orientation sensitive. The surface oxide layer remains unyielding until the metal-side cavities grow to a critical size above which the accumulated gas pressure become strong enough to blister the oxide layer.
Our findings have broad implications for coating performance in nuclear, petroleum, and transportation industries, and can help optimize the material design strategies to alleviate a broad range of hydrogen induced interface failures.
All authors for this work come from MSE, include Ph.D student Degang Xie, Dr. Zhangjie Wang, Prof. Jun Sun, Prof. Evan Ma, Prof. Ju Li and Prof. Zhiwei Shan. Fundings agiencies include the National Science Foundation of China, 973 Programs of China and 111 Project etc.
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