| Abstract Scope |
Microstructure evolutions in metastable beta titanium alloys can be tuned using a number of defect structures, such as grain boundary, dual-phase interface and pre-formed twin boundary. In our recent studies, we have found that the highly-indexed deformation twins in the cold-rolled metastable beta Ti-5Al-5Mo-5V-3Cr alloy (wt.%, Ti-5553) can assist the formation of hierarchical alpha microstructure during the subsequent heat treatment. In this work, we studied the nanoscale substructure in the hierarchical highly-indexed deformation twinning systems in the cold rolled Ti-5553 and Ti-24Nb-4Zr-8Sn (wt.%, Ti-2448) alloys using the diffraction contrast TEM and z-contrast aberration-corrected S/TEM. At the twin boundary, a nanoscale layer of metastable phase was observed and while in the interior of the twin, nanoscale metastable phases including omega phase and alpha” phase were characterized. The formation mechanisms of the hierarchical twinning in these titanium alloys will be discussed. This work is supported by the National Science Foundation, grant CMMI-2122272. |