The Role of Instabilities on Microstructural Evolution in Titanium Alloys

摘要技术概要：建议的工作包括五项任务，每项任务都与建议的既定目标有关，即详细了解各种结构不稳定性对钛合金微观结构演变的作用。这五项任务是：确定β基体中α的晶内成核、在先前β晶界上的他形α-钛的沉淀和钛合金中α侧板的形成、篮状组织微结构的形成的表征、（次生）α-钛在β-钛的肋中的应用，以及涉及钛合金中成核和相分离的统一机理模型的开发的总结任务。该研究将主要涉及应用新的最先进的表征工具来研究与多相钛合金微观结构演变相关的关键问题。重点将放在确定第二相成核的早期阶段的机制。此外，这些合金中不同相之间的元素分配和相间边界处的成分分布将以可达到的最高精度确定。一个并行的主题将是确定从两种不同类型的分析程序，即基于扫描透射电子显微镜的电子能量损失能谱法和三维局部电极原子探针断层摄影术获得的数据和信息的准确性、保真度和可解释性。非技术性总结：该计划的重点是一项研究，旨在制定一个详细的了解各种结构和成分的不稳定性对钛合金的微观结构演变的作用。这些合金已应用于许多产品领域，包括商用飞机喷气发动机，相反，生物医学工程，主要是因为它们具有吸引人的特性，并且因为它们具有相对低的密度。钛合金的充分利用需要操纵其微观结构以影响一系列性能组合，这反过来又需要详细了解这些微观结构演变所涉及的过程。关于钛合金中微观结构的演变，特别是关于第二相形核的早期阶段，有许多重要的未回答的问题。有必要集中努力，更透彻地了解这些进程，这是本建议的一个中心目标。最近显着增加的复杂程度的表征工具提出了一个真实的机会，使详细的观察微观结构演变的早期阶段，这里提出的大部分工作是基于这些新的和改进的材料表征技术的应用。

AbstractTECHNICAL SUMMARY: The proposed effort consists of five tasks, each bearing upon the stated aim of the proposal, namely to develop a detailed understanding of the role of various structural instabilities on microstructural evolution in titanium alloys. The five tasks are: determination of the factors governing intra-granular nucleation of alpha in the beta matrix, precipitation of allotriomorphic alpha-titanium on prior beta grain boundaries and formation of alpha sideplates in titanium alloys, characterization of the formation of the basket-weave microstructure, characterization of the formation of refined laths of (secondary) alpha-titanium in ribs of beta-titanium, and a summarizing task involving the development of a unified mechanistic model of nucleation and phase separation in titanium alloys. The research will involve primarily the application of novel state-of-the-art characterization tools to study critical issues related to microstructural evolution in multi-phase titanium alloys. Emphasis will be placed on determining the mechanisms underlying the early stages of second phase nucleation. In addition, the elemental partitioning between the different phases and compositional profiles at interphase boundaries in these alloys will be determined at the highest achievable accuracy. A concurrent theme will be to determine the accuracy, fidelity and interpretability of data and information obtained from the two different types of analytical procedures, namely scanning transmission electron microscopy-based electron energy-loss spectroscopy and 3D local electrode atom probe tomography. NON-TECHNICAL SUMMARY: The proposed program focuses on a study aimed at formulating a detailed understanding of the role of various structural and compositional instabilities on microstructural evolution in titanium alloys. These alloys have been applied in a number of product areas, including commercial aircraft jet engines and, in contrast, bio-medical engineering, largely because of a combination of attractive properties and because they are of relatively low density. The full exploitation of titanium alloys requires manipulation of their microstructures to affect a range of combinations of properties, and this in turn requires a detailed understanding of the processes involved in the evolution of these microstructures. There are many significant unanswered questions concerning the evolution of microstructures in titanium alloys, especially regarding the early stages of second phase nucleation. It is necessary to focus effort on developing a more thorough understanding of these processes, and this is a central objective of the present proposal. Recent significant increases in the level of sophistication of characterization tools present a real opportunity to make detailed observations of the early stages of microstructural evolution, and much of the work proposed here is based on the application of these new and improved techniques of materials characterization.