Superplastic Behavior and Microstructure Evolution of Fine-Grained TC4 Alloy Sheets
The superplastic behavior of fine-grained TC4 alloy sheets was investigated by the constant strain rate method at the temperature of 880-920 ℃ with the strain rate of 0.0005-0.005 s-1.Furthermore,the microstructure evolution was characterized during the super plastic deformation.The results reveal that with the increase in superplastic deformation temperature,the alloy undergoes conspicuous dynamic recrystallization,and the superplastic deformation mechanisms of the alloy also changes.At 880 ℃ with a strain rate of 0.001 s-1,the TC4 alloy exhibits a cooperative superplastic deformation mechanism involving grain boundary sliding,grain rotation and sliding.Under these conditions,the alloy achieves an elongation up to 1039％,accompanied by a notable strain sensitivity coefficient(m)of 0.51.In contrast,at 920 ℃ with a strain rate of 0.001 s-1,the alloy's superplasticity predominantly relies on grain boundary sliding and intragranular dislocation glide,resulting in a diminished elongation of 746％and a reduced m of 0.39.These findings elucidate the critical factors behind the varying superplastic performance of TC4 alloy under different temperatures and different strain rates,which is significant to further study the complex mechanical behavior and deformation mechanism of TC4 titanium alloy during superplastic deformation.
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