Probing the Early Stages of Second Phase Nucleation and Phase Separation in Titanium Alloys

技术：该计划重点研究钛合金中第二相形核和相分离的早期阶段。钛合金的充分开发需要操纵微观结构以影响一系列性能的组合，而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。关于钛合金微观组织的演变，特别是第二相形核和相分离的早期阶段，有许多重要的悬而未决的问题。有必要集中精力对这些过程进行更彻底的了解，这是本项目的中心目标。这项工作包括五项任务，每项任务都与项目的既定目标有关，即详细了解α-钛在贝塔基质中的成核过程，包括欧米伽相和贝塔相分离的影响以及群体和篮子编织微结构的形成。这五项任务是：表征在先前的β晶界上析出的异形α-钛，表征由异形α-钛形成魏氏组织片的特征，表征篮形组织形成的早期阶段，确定亚稳定相的影响，以及形成钛合金形核和相分离的统一观点。研究将涉及应用新的最先进的表征工具来研究与多相钛合金的微观结构演变有关的关键问题。重点将放在确定贝塔矩阵中第二相成核和相分离早期阶段的机制上。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摄影术。非技术性：这些合金已被应用于许多产品领域，包括商用飞机和发动机，相比之下，生物医学工程，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。该研究计划的目的是为预测材料的微结构/性能关系提供计算工具。这项研究的成功实施将产生新的科学，并对材料的工业开发产生重大影响，因此将对国家经济做出积极贡献。能够预测这些合金性能的研究工具的提供将对工业产生显著影响。教育推广计划将对鼓励不同种族背景的高中生进入科学和工程学科产生重大影响。由于其地理位置，工程学院和北卡罗来纳大学的材料科学与工程系处于独特的地位，可以为达拉斯-沃斯堡大都市综合体的劳动力提供此类教育和培训。

TECHNICAL: The program focuses on a study of the early stages of second phase nucleation and phase separation in Ti alloys. The full exploitation of Ti alloys requires manipulation of microstructure 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 Ti alloys, especially regarding the early stages of second phase nucleation and phase separation. It is necessary to focus effort on developing a more thorough understanding of these processes, and this is a central objective of this project. This effort consists of five tasks, each bearing upon the stated aim of the project, namely to develop a detailed understanding of the nucleation of alpha-Ti in a beta-matrix including the influence of the omega phase and beta phase separation and the formation of colony and basketweave microstructures. The five tasks are: characterization of the precipitation of allotriomorphic alpha-Ti on prior beta grain boundaries, characterization of the formation of Widmanstatten plates from allotriomorphic alpha-Ti, characterization of early stages of formation of basketweave microstructure, determination of the influence of metastable phases, and, forming a unified view of nucleation and phase separation in Ti alloys. Research will involve the application of novel state-of-the-art characterization tools to the study of critical issues related to microstructural evolution in multiphase Ti alloys. Emphasis will be placed on determining the mechanisms underlying the early stages of second phase nucleation and phase separation in the beta matrix. 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 the 3D local electrode atom probe tomography. NON-TECHNICAL: These alloys have been applied in a number of product areas, including commercial aircraft and engines and, in contrast, bio-medical engineering, largely because of a combination of attractive properties and because they are of relatively low density. The research program is aimed at the provision of computation tools for the prediction of microstructure/property relationships in materials. The successful implementation of the research will result in new science and have a significant impact on industrial exploitation of materials and hence will make a positive contribution to the Nation's economy. The provision of research tools capable of prediction of properties in these alloys will have a marked impact on industry. The educational outreach programs will have a significant influence on encouraging high school students with diverse ethnic backgrounds to enter science and engineering disciplines. Due to its geographic location, the College of Engineering and the Department of Materials Science and Engineering at UNT, are in a unique position to offer such education and training to the workforce of the Dallas-Fort Worth metroplex.