Experimental and Simulation Study of Compositional and Atomic-Scale Ordering Effects on Passivation in Fe-Cr and Ni-Cr Alloys

非技术摘要不锈钢和铁铬及镍铬合金以其优异的耐腐蚀性而闻名。这种行为源于在不锈钢表面上形成的保护性原子级保护氧化物层，如果以某种方式划伤或以其他方式破坏，则在几秒钟内在合金表面上重新形成。这种自修复行为可作为其他重要合金系统（包括铝和镁）的现代防腐蚀涂层方案开发的模型。该工作的主要目标是为不锈钢的行为开发简单的基于物理的模型，以便开发能够合理化现有数据并识别合金成分和原子尺度效应的设计方案，这些合金成分和原子尺度效应可用于设计具有上级耐腐蚀性的新合金系列。研究的范围，涉及实验室和计算工作，为本科生和研究生提供了材料电化学和腐蚀科学的基础培训的机会。这项研究的结果有望有助于国家关注的重要问题，这些问题与我们基础设施的健康以及用于汽车应用的轻质金属合金的开发有关，对于汽车应用，腐蚀是一个主要问题。铁合金的不锈钢般的行为需要铬，腐蚀科学中长期存在的未回答的问题是为什么？早期的工作连接的“关键”铬成分不锈钢一样的行为，以长期的渗滤阈值的随机结构，但最近的密度泛函计算，包括磁相互作用表明，铁铬合金是独特的，由于反转的符号的混合热发生在约10。%的Cr。 重要的是，穆斯堡尔和中子散射研究证实了这些计算对铁铬合金的预测，并揭示了原子尺度的有序性可以通过适当的热处理来“调整”。为了解开这个谜团，Fe-Cr和Ni-Cr合金的原子尺度结构正在被检查为组成和短程有序的函数。在固定的合金成分，短程有序的调整，通过改变合金的热处理。这项工作将通过使用扫描隧道显微镜对精心准备的合金表面进行原子尺度化学成像来表征短程有序。进行计算机模拟，以提取正则解理论参数，然后在蒙特卡洛重整化群计算中使用，以确定如何修改标准的逾渗阈值排序。采用电化学方法研究了成分和热处理对Fe-Cr和Ni-Cr合金钝化行为的影响。

NON-TECHNICAL ABSTRACTStainless steels and iron-chromium and nickel chromium alloys are well known for their excellent corrosion resistance. This behavior stems from a protective atomic-scale protective oxide layer that forms on the surface of stainless steels which if scratched or otherwise breached in some manner reforms within seconds on the surface of the alloy. This self-healing behavior serves as a model for the development modern corrosion protection coating schemes for other families of important alloy systems including aluminum and magnesium. The main objective of the work is to develop simple physically based models for the behavior of stainless steels in order to develop design schemes that can rationalize existing data and identify alloy compositions and atomic-scale effects that can be used to engineer new families of alloys with superior corrosion resistance. The scope of research, which involves laboratory and computational work, affords both undergraduate and graduate students the opportunity for fundamental training in materials electrochemistry and corrosion science. Results of this research are expected to contribute to important issues of national concern connected to both the well being of our infrastructure as well as the development of light-weight metallic alloys used in automotive applications for which corrosion is a major problem.TECHNICAL ABSTRACTWhile it is well known that 10-13 at.% chromium is required for stainless-like behavior of iron alloys, a long standing unanswered question in corrosion science is why? Early work connected "critical" Cr compositions for stainless-like behavior to long-ranged percolation thresholds for random structures but recent density functional calculations that incorporate magnetic interactions have shown that Fe-Cr alloys are unique owing to an inversion in the sign of the heat of mixing occurring at approximately 10 at. % Cr within a solid solution. Importantly, Mössbauer and neutron scattering studies have confirmed the predictions of these calculations for Fe-Cr alloys and revealed that atomic scale ordering can be "tuned" by suitable heat treatment. In order to unravel this mystery the atomic scale structure of Fe-Cr and Ni-Cr alloys is being examined as a function of composition and short-range order. At fixed alloy composition, short-range order is tuned by varying the heat treatment of the alloy. The work will characterize short-range order by atomic-scale chemical imaging of well-prepared alloy surfaces using scanning tunneling microscopy. Computer simulations are performed in order to extract regular solution theory parameters that are then used in Monte Carlo renormalization group calculations to determine how ordering modifies standard percolation thresholds. Electrochemical methods are used to measure how composition and heat treatment affect passivation behaviors in Fe-Cr and Ni-Cr alloys.