Abstract: Ultrafine-grained (UFG) titanium alloys exhibit enhanced strength and plasticity, higher high-cycle fatigue, and better corrosion resistance. Using the martensite microstructure as the precursor for thermal deformation can be an effective method for producing bulk UFG titanium alloys. In this study, the thermal compression processing parameters to produce UFG microstructure for a Ti6Al7Nb6Cu alloy were optimized and the mechanism for preparing UFG microstructure from martensite microstructure under the optimized parameters was systematically investigated. The microstructural evolution revealed that continuous dynamic recrystallization (CDRX) was the dominant mechanism during hot deformation of martensite. The angle (θ) between the lattice c-axis and the loading direction was calculated using Euler angles, and a quantitative relationship between θ and the Schmid factor was established to identify the activated slip systems in differently oriented martensite grains. Furthermore, the influence of activating different dislocation types on lattice rotation was explored by analyzing misorientation angles at dislocation pile-up boundaries. The results showed that activation of prismatic <a> dislocations most effectively promotes CDRX, followed by pyramidal <c+a> dislocations, while basal <a> dislocations contribute the least.

Key words: Ultrafine grained titanium, Nano lath martensite, Euler angle, Crystal orientation, Schmid factor