Corrosion Mechanisms in Amorphous-Partially Nanocrystalline Alloys

本项目旨在对纳米晶-非晶态合金中纳米晶的尺寸、成分和结构控制局部腐蚀和酸诱导去钝化性能的机制有一个基本的了解。正在考虑的合金包括锆等早期过渡金属、铁等晚期过渡金属和铝等简单金属元素。不同的成分在不同的温度下加工，以考察组成和结构的影响。这类材料表现出比传统多晶合金更高的机械强度和弹性系数，同时只要纳米晶的直径保持在20 nm以下，就能保持完全非晶态的优异的宏观耐腐蚀性。该项目的一个主要目标是研究与纳米晶尺寸相关的潜在方面，这些方面支配着对酸中一般腐蚀的抵抗力和局部腐蚀坑的形成。这项研究发展了有关保持这些纳米材料的耐腐蚀性和高机械强度的新的基础性认识。该项目包括广泛的电子显微镜的建模和实验工作。腐蚀性能将与对纳米尺度的电化学性质以及纳米尺度的组成和结构的理解相联系。因此，这项研究将为一类具有技术意义的材料的腐蚀行为提供新的纳米级结构-性能知识。这些新合金可能适用于需要高比强度和形状控制的部件，如MEMS和NEMS，这些部件几乎不能容忍腐蚀。这项研究的资助为研究生和本科生，包括未被充分代表的少数族裔提供了一个机会，以增进对腐蚀和材料科学多学科领域的了解和经验。这项研究对纳米晶-非晶合金的腐蚀机理有了新的认识，并努力避免在高强度和良好耐腐蚀性之间的权衡。除了科学上的进步，这项研究还将有助于开发MEMS和NEMS技术所需的具有优异耐蚀性的高强度合金。

This project is aimed at fundamental understandings of the mechanisms by which nanocrystal size, composition and structure control both localized corrosion and acid-induced depassivation properties in nanocrystalline-amorphous alloys. The alloys being considered include early transition metals such as zirconium, late transition metals such as iron and simple metal elements such as aluminum. Various compositions are processed at different temperatures to investigate the influence of composition and structure. This generic class of materials exhibits greater mechanical strengths and elastic moduli than conventional polycrystalline alloys while simultaneously retaining the excellent macroscopic corrosion resistance of the fully amorphous state as long as nanocrystals remain smaller than 20 nm in diameter. A major goal of the project is to investigate the underlying aspects associated with nanocrystal size that govern the resistance to general corrosion in acids and the formation of localized corrosion pits. This study develops new fundamental understanding involved with preserving corrosion resistance along with high mechanical strength of these nanomaterials. The project includes both modeling and experimental efforts with extensive electron microscopy. Corrosion properties will be linked with understandings of nm-scale electrochemical properties as well as nm-scale composition and structure. Thus, this research will provide new nanometer-scale structure-property knowledge regarding the corrosion behavior of a generic class of materials of technological significance. These new alloys may be useful in components requiring high specific strength and shape control such as MEMS and NEMS where little corrosion can be tolerated. The funding of this research provides an opportunity for graduate and undergraduate students including underrepresented minorities to develop understanding and experience in the multi-disciplinary fields of corrosion and materials science. This research develops new understanding of the corrosion mechanisms in nanocrystalline-amorphous alloys and strives to avoid the trade-off between high strength and good corrosion resistance in these new alloys. In addition to scientific advances, this research will be useful in the development of high strength alloys with excellent corrosion resistance required in MEMS and NEMS technologies.