The effects of different heat treatment temperature on microstructure of TC21 alloy after superplastic deformation were investigated by using superplastic tensile and triple heat treatment.The result shows that most ofαphase can be transformed intoβphase and transformedβstructure with annealing at above 940℃ during the first heat treatment.With the increase of the first heat treatment temperature

theβgrain boundary is grown gradually to completeness.In addition

the singleβphase equiaxial grain can be achieved by air cooling.The fine acicular secondaryαphase can be precipitated dispersedly fromβgrain during the second heat treatment.With the increase of the second anneal temperature

the amount of secondaryαphase and the size are increased.The smaller secondaryαphase can be precipitated from the gap of acicularαphase during the third heat treatment

and the secondaryαphase in the basketweave is coarsened with the increase of the temper temperature.