Time via temperature transformation curve of TC21 was investigated by simulation calculation using JMatPro software.Then the double annealing treatment of TC21 alloy was designed by time-temperature transformation curve.The results show that lamellarαphase is precipitated with the different temperature annealing treatment at a fixed deformation rate.The size ofαphase is increased with the increase of temperature.When the annealing temperature exceeds the phase transition point

Widmanstatten structure appears in the microstructure as a result of over-heating.The TC21 titanium alloy can not only generate the basket network structure but also retain some characteristics before annealing after secondary annealing.By observing the alloy microstructure after double annealing

fine sub-secondaryαphase is precipitated in theβmatrix

and the size of sub-secondaryαphase is increased with the temperature increase

which plays a certain role in microstructure and mechanical properties of the TC1 alloy.