Atomic-scale understanding of oxide growth and dissolution kinetics of Ni-Cr alloys

Passivation oxide formation is the key for corrosion control of metal alloys. The kinetics of competing oxide formation and dissolution determines alloy corrosion behaviors in aqueous solution. Despite the important role of the multi-component oxide evolution, little has been known on the kinetics from the atomistic level. We have built a computational framework that enables simulations of competing kinetic processes in multi-component oxides from first principles. The effects of applied voltage, pH and temperature on oxide growth, dissolution and reprecipitation can all be captured in this model. Combining with our experimental measurements on Alloy 22 and a Ni80%-Cr20% model alloy, we identified three voltage regimes with distinct oxide thicknesses and compositions.
The oxide energetics of various stoichiometries are calculated by the density functional theory (DFT). Then the obtained data are used to train a surrogate lattice Hamiltonian with the cluster expansion (CE) method. Finally, kinetic Monte Carlo (KMC) simulations are run with the cation hopping barriers calculated on-the-fly based on the local environments from the combination of the above Hamiltonian and the linear Brønsted−Evans−Polanyi (BEP) relation.

钝化氧化物的形成是控制金属合金腐蚀的关键。在水中，竞争性氧化物的形成与溶解的动力学决定了合金的腐蚀行为。尽管多组分氧化物的演变在腐蚀过程中扮演着至关重要的角色，但关于从原子层面上的动力学研究却鲜有涉猎。本研究构建了一个计算框架，该框架基于第一性原理，能够模拟多组分氧化物中竞争性动力学过程。在此模型中，施加电压、pH值和温度对氧化物生长、溶解和再沉淀的影响均得以捕捉。结合我们在合金22及Ni80%-Cr20%模型合金上的实验测量数据，我们确定了具有不同氧化物厚度和组成的三个电压区域。通过密度泛函理论（DFT）计算了各种化学计量比的氧化物能量学，随后利用所获得的数据，结合簇扩展（CE）方法对代理晶格哈密顿量进行训练。最终，通过基于上述哈密顿量与线性Brønsted−Evans−Polanyi（BEP）关系的局部环境，即时计算阳离子跳跃势垒，运行了动力学蒙特卡洛（KMC）模拟。