Non-Classical Precipitation Mechanisms in Titanium Alloys

技术摘要：该计划重点研究金属合金中固态沉淀的新的非经典机制，主要集中在钛(钛)合金上。该计划的意义来自于这些合金的组织和性能之间的相互关系，这些相互关系已经通过实验确定。为了减少材料开发和优化的时间和成本，这些数量将在未来通过计算模型进行预测。这种微结构演化计算模型的成功发展，关键取决于对成核过程的准确描述，以便这些模型可以尽可能地具有物理相关性。因此，建议的方案的作用是提供对影响成核过程的因素的如此准确的描述。与传统的理解相反，钛合金中特定的非经典析出机制是，α相在钛中的精细分布，通过伪旋节状机制从贝塔相的基质中析出，以及欧米伽析出的耦合混合模式机制，同时发生位移和扩散过程。还将研究在以欧米伽相为先驱体的贝塔基质中形成更精细分布的α-钛的情况。大体上，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沉淀机制相关的关键问题。重点将放在确定第二阶段早期成核的潜在机制上。此外，将以最高的准确度和精密度确定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。一个同时的主题是确定从两种不同类型的分析方法获得的数据和信息的准确性、保真度和可解释性，即基于扫描电子显微镜的电子能量损失能谱和X射线能量色散能谱，以及局部电极原子探针层析。非技术摘要：拟议的研究计划涉及旨在形成对钛合金中新的非经典析出机制的详细了解的重点工作。这项拟议的研究工作汇集了最先进的表征工具，用于解决与钛合金相关的这些机制。虽然拟议方案的重点是钛合金，但应该指出，正在研究的机制，特别是通过小幅度成分波动调节的非经典析出，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研究工具，这些工具将适用于钛合金以外的各种金属材料。拟议的研究计划是旨在为预测材料微结构演变和微结构/性能关系提供计算工具的更大努力的一部分，是材料基因组倡议(MGI)和综合计算材料工程(ICME)倡议下的国家努力的组成部分。这项拟议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。为此，一个非常成功的外展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材料世界。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-沃斯堡大都会建筑群的员工提供此类教育和培训。

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.