Role of Competitive Surface Chemical Reactions in Ductility of Intermetallics

竞争性表面化学反应在金属间化合物延展性中的作用

• 批准号: 9410701
• 负责人: Yip-Wah Chung
• 金额: $ 19.74万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-08-01 至 1997-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9410701&HistoricalAwards=false
• 关键词: Role; Competitive; Surface; Chemical; Reactions

9410701 Chung In spite of the many interesting properties of intermetallics that make them attractive as high temperature materials, they share one common disadvantage: brittle behavior in room temperature air. There have been numerous studies in the last ten years to explore different ways to ductilize this class of materials. Recent studies suggest that intermetallic alloys such as Nickel-Aluminide (Ni3Al) are intrinsically ductile, and their brittleness is a result of hydrogen embrittlement (the hydrogen produced by reactions between water vapor in air and fresh intermetallic surfaces exposed during deformation). However, other intermetallics such as Nickel-Iron (Ni3Fe) do not appear to exhibit any moisture-induced embrittlement. It is hypothesized that if the water dissociation reaction to produce hydrogen is quenched in some way by the presence of oxygen, there will be no hydrogen embrittlement, and the material will show improved ductility. To test this hypothesis, detailed surface science investigations of the interactions between water vapor and clean surfaces of intermetallic alloys, with and without the presence of oxygen, are planned. Using single crystals of the intermetallic alloy nickel-aluminum-titanium, Ni3(Al,Ti), the room temperature sticking probability of water vapor on various crystal faces will be measured and compared with oxygen. Vibration spectroscopy and thermal desorption are used to determine on which crystal face the adsorbed water dissociates to form hydrogen and if such dissociation is affected by co-adsorbed oxygen. To understand why Ni3Fe polycrystals do not suffer moisture-induced embrittlement, similar studies are performed to determine if oxygen out competes water vapor for available adsorption sites and if co-adsorption of water vapor and oxygen results in the formation of surface hydroxyls instead of hydrogen. %%% These studies provide the basic framework to understand and possibly control moisture-induc ed embrittlement in this important class of materials. ***

9410701尽管金属间化合物具有许多有趣的性质，使其成为具有吸引力的高温材料，但它们有一个共同的缺点：在室温空气中的脆性行为。在过去的十年里，有许多研究探索了利用这类材料的不同方法。最近的研究表明，镍铝化物(Ni3Al)等金属间化合物合金具有本质的延展性，它们的脆性是氢脆(空气中的水蒸气与变形过程中暴露的新鲜金属间化合物表面发生反应产生的氢气)的结果。然而，其他金属间化合物，如镍-铁(Ni3Fe)，似乎没有表现出任何湿气诱导的脆化。假设如果水的分解反应产生氢的反应被氧以某种方式熄灭，就不会有氢脆，材料将表现出更好的延展性。为了验证这一假设，计划对金属间化合物合金在有氧和无氧情况下水蒸气和清洁表面之间的相互作用进行详细的表面科学研究。利用金属间化合物镍铝钛单晶Ni3(Al，Ti)，测量了水蒸气在不同晶面上的室温粘附率，并与氧气作了比较。振动光谱和热脱附被用来确定吸附的水在晶面上解离形成氢，以及这种解离是否受共吸附的氧的影响。为了了解为什么Ni3Fe多晶不会受到湿气诱导的脆化，我们进行了类似的研究，以确定氧气是否会竞争水蒸气对可用吸附位置的竞争，以及水蒸气和氧气的共吸附是否会导致表面羟基而不是氢的形成。%这些研究为理解并可能控制这类重要材料中由水分引起的脆化提供了基本框架。***