Evolution of α phase morphology in hot-rolling TC21 titanium alloy plate

The microstructure evolution and mechanisms of globularization of TC21 titanium alloy with lamellar structure were investigated during hot rolling in the β phase and α+β phase. The results show that the prominent effect of hot working parameters on the break-up and globularization of TC21 titanium alloy with lamellar structure is found. The α lamellar structure along the paralleling rolling orientation and adjacent grain boundaries is broken up and globularized and the intragranular α lamellar is buckled and kinked when TC21 titanium alloy is processed in β phase region (990°C) at strain no less than 0.51 and at 950°C and strain 0.92. When TC21 titanium alloy is deformed at 910°C and 870°C, α lamellar is buckled and kinked to become accordion. Then, by TEM analysis, it is found that the mechanism of globularization of TC21 titanium alloy with α lamellar is a comprehensive process that is firstly the formation of α/α interface by dynamic recovery or boundary splitting, secondly the disintegrating of α lamellar due to diffusing, and finally the globularization of α lamellar by termination migration.