Abstract
The new near-α TNW700 titanium alloy is a potential candidate material for high performance ultra-sonic/hypersonic aircrafts,which is designed for short-term service at 700℃.This study systematically investigated the superplastic deformation microstructure evolution and mechanism of TNW700 alloy at different strain rates and true strains at 925℃.Results show that TNW700 alloy exhibits excellent super-plastic behavior in a constant strain rate range of 0.0005-0.005 s-1 with elongation above 400％.The peak stress decreases with decreasing strain rate,which is related to the increase ofβ-phase volume fraction caused by the increase of thermal exposure time.In addition,significant strain hardening is observed in early-middle stage of superplastic deformation,and flow softening is followed in middle-late stage.To ra-tionalize these complex flow behaviors,electron backscatter diffraction(EBSD)and high resolution trans-mission electron microscopy(HRTEM)were used to characterize the microstructure.Strain hardening is correlated to the synergistic effect ofβ grain growth,dislocation accumulation,silicide precipitate,and solid solution strengthening of α phase.Continuous dynamic recrystallization(CDRX)induced the frag-mentation of primary α grains in middle-late stage of superplastic deformation,and the refinement of αgrains,the increase of β phase volume fraction and dynamic dislocation recovery are main causes of high strain softening.In addition,EBSD and TEM observations confirmed texture randomization,fine equiaxed primary α grains and intragranular dislocation movement,indicating that grain boundary sliding(GBS)accommodated by dislocation sliding/climb is the dominant superplastic deformation mechanism of TNW700 alloy.
基金项目
authors would like to acknowledge the support to this re-search work from the Aeronautical Science Foundation of China(201936051001)
NETL
NSTL
万方数据