Influence of Lattice Instabilities on Microstructural Evolution in Metastable Ti Alloys

The existence of several lattice instabilities in metastable Ti alloys is confirmed by direct observation using aberration-corrected scanning transmission electron microscopy. These include the ω phase, which is shown to be the product of a mixed-mode phase transformation, the O’ phase, and the O” phase. Their role on microstructural evolution in these metastable alloys has been determined by a combination of experiment and computational materials science. It will be shown that three distinct size distributions of the α phase may be effected by either quenching from above the β-transus followed by continuous heating, or by step-quenching to given temperatures followed by isothermal annealing. These distributions have been termed refined, more refined and super-refined. Preliminary assessments of the mechanical properties exhibited by samples possessing these microstructures will be presented. This research has been sponsored by the NSF, under grants DMR-1309270 and DMREF DMR-1435483.