The effects of superplastic compression deformation and multiple annealing heat treatment on microstructure evolution of TC21 titanium alloy were investigated.The results reveal that the number of large deformation zoneα-phase transferred to metastableβphase is more than that free deformation zone at superplastic compression deformation in the two-phase region.When deformed in theβsingle-phase region

theβ-phase grain size is increased with the deformation temperature increase.After the double annealing under the same deformation condition

although the size of the precipitated acicularαphase is increased with the increase of the annealing time

the formed basket structure is more interwoven.The basket structure formed by triple annealing is finer than that of ones by double annealing

and the second heat treatment temperature is lowered

so the size of the precipitated acicularαphase can be reduced remarkably.It is found that with the increase of superplastic deformation temperature

the size of the precipitated acicularαphase is increases continuously regardless of double annealing or triple annealing

indicating that the deformation temperature before annealing has a significant effect on the microstructure after annealing.