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

Ohio State University Research Foundation -Do Not Use, Columbus OH

Investigators

Abstract

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.