The Role of Surface Reactions and Hydrogen Surface Diffusivity on the Environmental Embrittlement of (Ni,Fe)Ti Alloys

这项资助主要针对金属间化合物的湿气脆化问题，重点是(Ni，Fe)Ti。尽管(Ni，Fe)钛合金各组元对水有反应能力，但只要Fe含量小于9a/o，就不会被水分脆化，但当Fe含量较高时，它们会因水分而严重脆化。这就要求对传统上公认的金属间化合物湿致脆化机制进行详细的重新审视。也就是说，除了水在金属间化合物表面上解离产生原子氢之外，还需要哪些其他因素来产生湿气诱导的脆化？利用表面科学方法，研究了不同取向和Fe浓度的(Ni，Fe)Ti单晶表面的水蒸气反应性。目的是确定是否发生水解离产生原子氢，如果发生，原子氢与金属间化合物表面的结合强度有多大。对于更好的理解，最重要的是使用电子刺激脱附来定量确定氢在这些表面上的扩散系数。这些研究应提供必要的原子尺度细节，以解释金属间化合物中水分诱导的脆性、表面反应性和原子氢的迁移率之间的相互关系。金属间化合物合金作为高温结构金属合金具有广阔的应用前景。一个潜在的问题是金属间化合物与环境的反应性。这笔赠款探索了这个问题的一个方面。*

0095381Chung This grant deals with the fundamental issues surrounding the moisture-induced embrittlement of intermetallic alloys with a focus on (Ni,Fe)Ti. In spite of the reactivity of individual components to water, (Ni,Fe)Ti alloys are not embrittled by moisture, as long as the Fe concentration is less than 9 a/o. However, they become severely embrittled by moisture at higher Fe concentrations. This calls for a detailed re-examination of the traditionally accepted mechanism of moisture-induced embrittlement of intermetallics. That is, in addition to the dissociation of water to produce atomic hydrogen on intermetallic surfaces, what other factors are required to produce moisture-induced embrittlement? Using a surface science approach, this study looks at the water vapor reactivity of single crystal (Ni,Fe)Ti surfaces of different orientations and Fe concentrations. The objective is to determine whether or not water dissociation to produce atomic hydrogen occurs, and, if so, how strongly the atomic hydrogen is bound to the intermetallic surface. Most important to improved understanding is a quantitative determination of the diffusivity of hydrogen on these surfaces using electron-stimulated desorption. These investigations should provide the necessary atomic scale details to explain the inter-relationships among moisture-induced embrittlement, surface reactivity, and mobility of atomic hydrogen in intermetallic alloys. %%%Intermetallic alloys offer promise as high temperature structural metal alloys. One potential problem is the reactivity of intermetallics with the environment. This grant explores one facet of this problem.***