The Role of Instabilities on Microstructural Evolution in Titanium Alloys

技术摘要：拟议的工作包括五项任务，每项任务都与提议的既定目标有关，即详细了解各种结构不稳定性在钛合金组织演变中的作用。这五项任务是：确定控制贝塔基体中α的晶内形核的因素，在先前的贝塔晶界析出异形的α-钛和形成钛合金中的α侧板，表征编织篮状组织的形成，表征在贝塔钛筋中形成(二次)α-钛的细小板条的特征，以及涉及建立钛合金形核和相分离的统一机制模型的总结任务。这项研究将主要涉及应用最新的最先进的表征工具来研究与多相钛合金组织演变相关的关键问题。重点将放在确定第二阶段早期成核的潜在机制上。此外，这些合金中不同相之间的元素分配和相界面上的成分分布将以最高的精度确定。同时进行的一个主题是确定从两种不同类型的分析程序获得的数据和信息的准确性、保真度和可解释性，这两种不同类型的分析程序是：基于扫描电子显微镜的电子能量损失光谱分析和三维局部电极原子探针断层扫描。非技术性摘要：拟议的计划侧重于一项研究，旨在详细了解各种结构和成分不稳定性在钛合金微观结构演变中的作用。这些合金已经应用于许多产品领域，包括商用飞机喷气发动机和生物医学工程，这主要是因为它们具有诱人的性能组合，而且它们的密度相对较低。钛合金的充分开发需要操纵其微观结构以影响一系列性能组合，而这反过来又需要详细了解这些微结构演变所涉及的过程。关于钛合金组织的演变，特别是第二相形核的早期阶段，有许多重要的问题没有得到解答。有必要集中努力更彻底地了解这些进程，这是本提案的中心目标。最近表征工具复杂程度的显著提高为详细观察微结构演变的早期阶段提供了一个真正的机会，这里提出的许多工作都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.