The direct three-dimensional characterization and visualization of structural materials using characterization techniques such as the DualBeam™ Focused Ion Beam (DB-FIB) instrument has resulted in a significant increase in the level of understanding of materials microstructures. Indeed, visualizations of three-dimensional datasets can provide directly interpretable results (both quantitatively and qualitatively) regarding the true morphology and distribution of phases. This thesis, in part, develops a methodology and examines the accuracy of the quantitative measurements and the clarity of the qualitative descriptions afforded by the application of the DualBeam™ FIB as a tool for the three-dimensional characterization of Ti-based alloys.
The Dual Beam™ FIB systems also provide a method for site-specific TEM sample preparation which greatly reduced the amount of time necessary to isolate desired features. This method creates relatively significant damage during the sputtering process and subsequently hinders further analysis and in some cases prevents further analysis. A methodology for predictive, low – energy ion milling technique for optimal HR-STEM and HR-TEM sample preparation is developed in conjunction with the Fischione NanoMill™.
The methodologies developed in this work have been applied to binary Ti – Mo alloys to prove their validity. β-Ti alloys exhibit several complex and competing phase transformations such as nucleation of the metastable omega-phase at low to intermediate temperatures and β-phase separation at intermediate temperatures. Both omega-phase and/or beta - phase separation have been proposed as heterogeneous sites assisting in intragranular nucleation and growth of the α-phase.
Through studying the commercial alloy the model binary Ti – Mo system, an attempt is made to understand the stability of the ω-phase and factors governing the nucleation of the α-phase at low to intermediate temperatures. For the first time, using a combination of HR - STEM, HR-TEM, and 3DAP tomography the structure and composition of the omega phase, as well as the alpha/beta, omega/beta interfaces are investigated for various thermal histories.