Non-Classical Precipitation Mechanisms in Titanium Alloys

技术概述：该计划侧重于金属合金中固态沉淀的新型非经典机制，主要关注钛（Ti）合金。所提出的程序的意义源于这些合金的微观结构和性能之间的相互关系，这些相互关系已被实验确定。为了减少材料开发和优化的时间和成本，未来这些数量将成为计算模型预测的主题。这种微观结构演化的计算模型的成功发展关键取决于对成核过程的准确描述，以便这些模型可能尽可能地与物理相关。因此，所提出的程序的作用是对影响成核过程的因素提供如此准确的描述。与传统的理解不同，本文研究的具体非经典析出机制是：由β相的基体通过伪旋轴机制和omega析出的耦合混合模式机制析出的α相在Ti中的精细分布，同时发生位移和扩散过程。以相为前驱体在β基体中形成更精细的α - ti分布也将被研究。主要的研究将涉及应用新的最先进的表征工具来研究与两种新的非经典降水机制相关的关键问题。重点将放在确定第二阶段成核早期阶段的机制。此外，这些合金中不同相之间的元素分配和相间边界的成分分布将以可达到的最高精度和精度确定。同时的主题将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，即基于扫描透射电子显微镜的电子能量损失光谱和x射线能量色散光谱，以及局部电极原子探针层析成像。非技术总结：提出的研究计划包括一个集中的努力，旨在制定一个详细的了解新的非经典的沉淀机制在钛合金。提议的研究工作汇集了最先进的表征工具，以解决与钛合金相关的这些机制。虽然该计划的重点是钛合金，但应该指出的是，正在研究的机制，特别是通过小幅度成分波动介导的非经典沉淀，一般适用于其他金属材料，原则上也适用于陶瓷和半导体系统。此外，该计划还将导致开发有用的纳米级表征新研究工具，这将适用于钛合金以外的广泛金属材料。拟议的研究计划是一项更大努力的一部分，旨在提供用于预测材料微观结构演变和微观结构/性能关系的计算工具，是材料基因组计划（MGI）和综合计算材料工程（ICME）计划下国家努力的组成部分。所提议的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，从而将对国家经济作出积极贡献。提供能够预测这些合金性能的研究工具将对工业产生显著影响。教育外展项目将对鼓励不同种族的高中生进入理工科产生重大影响。为此目的，一个非常成功的外联项目包括在哥伦布科学与工业中心（COSI）进行互动演示，让所有年龄段的儿童和学生通过扫描电子显微镜体验物质世界。由于其地理位置，UNT的工程学院和材料科学与工程系处于独特的地位，可以为达拉斯-沃斯堡大都市的劳动力提供这样的教育和培训。

TECHNICAL SUMMARY:The proposed program focuses on novel non-classical mechanisms of solid-state precipitation in metallic alloys, with a primary focus on titanium (Ti) alloys. The significance of the proposed program stems from the interrelationship between microstructure and properties in these alloys where these interrelationships have been determined experimentally. To reduce the time and costs of materials development and optimization, in the future these quantities will be the subject of prediction by computational models. The successful development of such computational models of microstructural evolution depends critically on accurate descriptions of the nucleation process, so that the models may be as physically relevant as possible. Hence, it is the role of the proposed program to provide such accurate descriptions of the factors that influence the nucleation process. The specific non-classical mechanisms of precipitation in Ti alloys that will form the subject of the proposed research are, the refined distribution of the alpha phase in Ti precipitated from a matrix of the beta phase by the pseudo-spinodal mechanism and the coupled mixed-mode mechanism of omega precipitation, with concurrently occurring displacive and diffusional processes, in contrast to the legacy understanding. The formation of an even more refined distribution of alpha-Ti in a beta-matrix with the omega phase as a precursor will also be investigated. In the main, the research will involve the application of novel state-of-the-art characterization tools to the study of critical issues related to the two novel non-classical precipitation mechanisms. 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 and precision. 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 x-ray energy dispersive spectroscopy, and the local electrode atom probe tomography.NON-TECHNICAL SUMMARY:The proposed research program involves a focused effort aimed at formulating a detailed understanding of novel non-classical precipitation mechanisms in Ti alloys. The proposed research effort brings together state-of-the-art characterization tools for addressing these mechanisms associated with Ti alloys. While the focus of the proposed program is on titanium alloys, it should be noted that the mechanisms being investigated, especially non-classical precipitation mediated via compositional fluctuations of small amplitude, are applicable in general to other metallic materials, and, in principle, also to ceramic and semiconducting systems. Additionally, the program will also result in the development of useful new research tools for nanoscale characterization which will be applicable to a wide range of metallic materials beyond Ti alloys. The proposed research program is part of a larger effort aimed at the provision of computation tools for the prediction of microstructure evolution and microstructure/property relationships in materials, an integral part of the national efforts under the Materials Genome Initiative (MGI) and the Integrated Computational Materials Engineering (ICME) initiative. The successful implementation of the proposed 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. To that end, a very successful outreach program has involved interactive demonstrations at the Columbus' Center of Science and Industry (COSI) where children and students of all ages experience the world of materials through scanning electron microscopes. 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.