Song Boao, Yang Yong, Rabbani Muztoba, Yang Timothy T, He Kun, Hu Xiaobing, Yuan Yifei, Ghildiyal Pankaj, Dravid Vinayak P, Zachariah Michael R, Saidi Wissam A, Liu Yuzi, Shahbazian-Yassar Reza
Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, United States.
ACS Nano. 2020 Nov 24;14(11):15131-15143. doi: 10.1021/acsnano.0c05250. Epub 2020 Oct 20.
Although high-entropy alloys (HEAs) have shown tremendous potential for elevated temperature, anticorrosion, and catalysis applications, little is known on how HEA materials behave under complex service environments. Herein, we studied the high-temperature oxidation behavior of FeCoNiCuPtHEA nanoparticles (NPs) in an atmospheric pressure dry air environment by gas-cell transmission electron microscopy. It is found that the oxidation of HEA NPs is governed by Kirkendall effects with logarithmic oxidation rates rather than parabolic as predicted by Wagner's theory. Further, the HEA NPs are found to oxidize at a significantly slower rate compared to monometallic NPs. The outward diffusion of transition metals and formation of disordered oxide layer are observed in real time and confirmed through analytical energy dispersive spectroscopy, and electron energy loss spectroscopy characterizations. Localized ordered lattices are identified in the oxide, suggesting the formation of FeO, CoO, NiO, and CuO crystallites in an overall disordered matrix. Hybrid Monte Carlo and molecular dynamics simulations based on first-principles energies and forces support these findings and show that the oxidation drives surface segregation of Fe, Co, Ni, and Cu, while Pt stays in the core region. The present work offers key insights into how HEA NPs behave under high-temperature oxidizing environment and sheds light on future design of highly stable alloys under complex service conditions.
尽管高熵合金（HEAs）在高温、防腐和催化应用方面已展现出巨大潜力，但对于HEA材料在复杂服役环境中的行为却知之甚少。在此，我们通过气室透射电子显微镜研究了FeCoNiCuPtHEA纳米颗粒（NPs）在常压干燥空气环境中的高温氧化行为。研究发现，HEA NPs的氧化受柯肯达尔效应控制，氧化速率呈对数关系，而非瓦格纳理论预测的抛物线关系。此外，与单金属NPs相比，HEA NPs的氧化速率明显更慢。通过能量色散谱分析和电子能量损失谱表征，实时观察到了过渡金属的向外扩散以及无序氧化层的形成。在氧化物中识别出了局部有序晶格，表明在整体无序的基体中形成了FeO、CoO、NiO和CuO微晶。基于第一性原理能量和力的混合蒙特卡罗模拟和分子动力学模拟支持了这些发现，并表明氧化促使Fe、Co、Ni和Cu发生表面偏析，而Pt则留在核心区域。本研究为HEA NPs在高温氧化环境中的行为提供了关键见解，并为复杂服役条件下高稳定性合金的未来设计提供了思路。
