Interfacial Structure and Processes in Lamellar Titanium Aluminide Alloys

层状铝化钛合金的界面结构和过程

• 批准号: 0072721
• 负责人: Mark Aindow
• 金额: $ 43.18万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-07-01 至 2006-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0072721&HistoricalAwards=false
• 关键词: Interfacial; Structure; Processes; Lamellar; Titanium

0072721AindowThis research develops a fundamental understanding of the effects of interfacial structure on the evolution of the lamellar microstructure in TiAl-based alloys and on the subsequent mechanical behavior of alloys that exhibit this microstructure. The lamellar gamma/alpha2 interfaces have been studied in great detail both by conventional transmission electron microscopy (TEM) and by high-resolution electron microscopy (HREM). In a recent HREM study of a low-misfit lamellar alloy, this investigator has shown that the steps on these interfaces can exhibit a greater diversity of heights and Burgers vectors than has been reported previously. Moreover, he found that the Burgers vectors exhibited by the steps varied with both the height and sense of the step. In each case these Burgers vectors were consistent with the steps being perfect interfacial disconnections as described by Pond's topological theory of interfacial defects, not Shockley partial dislocations as proposed previously. These observations have wide-ranging consequences for any defect-mediated interfacial processes in such alloys since one would expect the behavior of perfect disconnections to be radically different from that of Shockley partials in the same interface. In this research, defect-mediated interfacial processes in lamellar TiAl-based alloys are investigated by measuring changes in the interfacial defect configurations as a function of thermomechanical history. The character of the defects are determined by using the topological theory of interfacial defects to interpret detailed TEM and/or HREM observations, and the associated flux analysis are used to identify the factors controlling line defect motion. This approach addresses four key topics: (1) The mechanism for the formation of gamma lamellae; (2) The interaction of interfacial step defects; (3) Slip transmission through gamma/alpha2 interfaces; and (4) Introduction of misfit dislocations at gamma/alpha2 interfaces.%%%It is anticipated that by elucidating the mechanisms for the defect-mediated interfacial processes in TiAl intermetallic alloys the program will have broad technological impact for high temperature structural applications, particularly in the aerospace sector. This understanding is essential in determining alloy development strategy for the next generation of lamellar TiAl-based alloys. This program is the first instance where the topological theory is used to interpret detailed TEM/HREM data from engineering alloys. Thus, it is anticipated that the work will have broader scientific impact in that it will constitute a model study to demonstrate the efficacy of the approach. This program provides integrated training for two graduate students and combines the fundamental rigor of crystallographic analyses with transferable experimental skills. It also provides the students with the opportunity to participate in an international collaboration with scientists in England. ***

这项研究对TiAl基合金中界面结构对片层组织演变的影响以及对呈现这种组织的合金的后续力学行为有了一个基本的了解。用常规的透射电子显微镜和高分辨电子显微镜对层状的伽马/α2界面进行了详细的研究。在最近的一项对低失配片层合金的HREM研究中，这位研究人员表明，这些界面上的台阶可以显示出比以前报道的更大的高度和Burgers矢量的差异。此外，他还发现，台阶所表现出的Burgers矢量随台阶的高度和感觉而变化。在每种情况下，这些Burgers矢量都与Pond的界面缺陷拓扑理论所描述的完美界面脱节的步骤一致，而不是先前提出的Shockley部分位错。这些观察结果对这类合金中任何由缺陷介导的界面过程都有广泛的影响，因为人们预计完美断开的行为与同一界面上的Shockley分项的行为完全不同。在这项研究中，通过测量界面缺陷构型随热机械历史的变化，研究了层状TiAl基合金中缺陷介导的界面过程。用界面缺陷的拓扑理论解释了详细的透射电子显微镜和/或高分辨电子显微镜观察，确定了缺陷的性质，并用关联通量分析确定了控制线缺陷运动的因素。这一方法解决了四个关键问题：(1)伽马片层的形成机制；(2)界面台阶缺陷的相互作用；(3)通过伽马/α2界面的滑移传输；(4)在伽马/α2界面引入失配位错。%预计，通过阐明TiAl金属间化合物合金中缺陷介导的界面过程的机制，该程序将对高温结构应用产生广泛的技术影响，特别是在航空航天领域。这一认识对于确定下一代片层TiAl基合金的合金发展战略是至关重要的。该程序是首次将拓扑理论用于解释工程合金的详细的透射电子显微镜/高分辨电子显微镜数据。因此，预计这项工作将产生更广泛的科学影响，因为它将构成一项示范研究，以证明该方法的有效性。该计划为两名研究生提供综合培训，并将晶体分析的基本严谨性与可移植的实验技能相结合。它还为学生提供了与英国科学家参与国际合作的机会。***