Non-Classical Precipitation Mechanisms in Titanium Alloys

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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.