Rugolo J, Erlebacher J, Sieradzki K
Arizona State University, Tempe, Arizona 85287-6106, USA.
Nat Mater. 2006 Dec;5(12):946-9. doi: 10.1038/nmat1780. Epub 2006 Nov 12.
De-alloying is the selective dissolution of one or more of the elemental components of an alloy. In binary alloys that exhibit complete solid solubility, de-alloying of the less noble component results in the formation of nanoporous metals, a materials class that has attracted attention for applications such as catalysis, sensing and actuation. In addition, the occurrence of de-alloying in metallic alloy systems under stress is known to result in stress-corrosion cracking, a key failure mechanism in fossil fuel and nuclear plants, ageing aircraft, and also an important concern in the design of nuclear-waste storage containers. Central to the design of corrosion-resistant alloys is the identification of a composition-dependent electrochemical critical potential, Vcrit, above which the current rises dramatically with potential, signalling the onset of bulk de-alloying. Below Vcrit, the surface is passivated by the accumulation of up to several monolayers of the more noble component. The current understanding of the processes that control Vcrit is incomplete. Here, we report on de-alloying results of Ag/Au superlattices that clarify the role of pre-existing length scales in alloy dissolution. Our data motivated us to re-analyse existing data on critical potentials of Ag-Au alloys and develop a simple unifying picture that accounts for the compositional dependence of solid-solution alloy critical potentials.
脱合金化是指合金中一种或多种元素成分的选择性溶解。在具有完全固溶体的二元合金中，较不活泼成分的脱合金化会导致纳米多孔金属的形成，这类材料在催化、传感和驱动等应用中受到了关注。此外，已知在应力作用下金属合金系统中发生脱合金化会导致应力腐蚀开裂，这是化石燃料和核电站、老旧飞机中的关键失效机制，也是核废料储存容器设计中的一个重要问题。耐腐蚀合金设计的核心是确定一个与成分相关的电化学临界电位Vcrit，高于该电位时电流会随电位急剧上升，表明整体脱合金化的开始。在Vcrit以下，表面会被多达几个单分子层的较活泼成分积累所钝化。目前对控制Vcrit的过程的理解并不完整。在这里，我们报告了Ag/Au超晶格的脱合金化结果，这些结果阐明了预先存在的长度尺度在合金溶解中的作用。我们的数据促使我们重新分析关于Ag-Au合金临界电位的现有数据，并开发出一个简单的统一图景，该图景解释了固溶体合金临界电位的成分依赖性。
