A new microstructural refinement mechanism of ultra-large β grains in near-β titanium alloys during primary hot-working

In this work, the multi-step hot-working of a near-beta titanium alloy, Ti-55511 alloy with centimeter-sized grains, was performed at 1170 degrees C. It was confirmed that the static/metadynamic recrystallization during interpass annealing was the primary mechanism responsible for the microstructural refinement. Meanwhile, a new breakdown mechanism of the ultra-large beta grains with (001) preferential orientation was observed during deformation, which was essentially different from the traditional discontinuous or continuous dynamic recrystallization. That is, new grain boundaries and even boundary networks were produced interconnecting the corners/protrusions of the (001) -orientated grains through a low-angle grain boundary merging mechanism, which progressively severed the large beta grains into smaller ones. Such a breakdown mechanism may be an important complement for microstructural refinement during primary hot-working, which allowed the breakdown of the ultra-large beta grains under fairly low strain level.