| TC4 titanium alloy is widely used in the aerospace field due to its advantages of low density,high strength,and good corrosion resistance.Moreover,the 3D bending structural components of profiles made of it have become important lightweight key skeleton components in the aerospace field.However,titanium alloys have poor formability at room temperature,making it difficult to meet the forming accuracy and usage requirements.Therefore,it is necessary to use hot-forming technology to process titanium alloys.Under high-temperature conditions,the 3D stretch-bending of titanium alloy profiles is subjected to both tensile and bending loads,resulting in complex deformation conditions and involving many issues such as thermal coupling.Therefore,this article conducted a study on the tensile-bending deformation behavior of TC4 titanium alloy under high-temperature conditions,exploring the internal deformation mechanism and forming laws.On this basis,a two-phase crystal plasticity model of TC4 titanium alloy was constructed,and the real-time microstructure evolution law of TC4 titanium alloy during high-temperature deformation was deeply studied,revealing the high-temperature microstructure deformation mechanism of TC4 titanium alloy.The specific research is as follows:Based on a uniaxial hot tensile testing platform,uniaxial tensile tests were conducted on TC4 titanium alloy hot tensile specimens at different temperatures and strain rates to investigate the effects of temperature and strain rate on the rheological stress and mechanical properties of the material.The experimental results indicate that under the same strain rate conditions,the increasing temperature can significantly reduce the yield strength of TC4 titanium alloy.At the same temperature,as the strain rate increases,the stress value gradually increases.Higher yield strength and tensile strength can be obtained by increasing the strain rate and decreasing the temperature appropriately.In addition,based on the multi-point 3D hot stretch-bending process and its forming equipment,the effects of pre-stretching,post-stretching,and temperature on the springback deformation behavior of L-shaped cross-section profiles are studied.It was found that forming temperature is the most important factor affecting springback deformation.When the temperature is constant and the pre-stretching amount is 100%ε_s,and the post-stretching amount is 20%ε_s,the profile reaches the optimal forming state.On this basis,the microstructure of TC4 titanium alloy material was characterized,and the internal mechanisms of its uniaxial hot tensile deformation behavior and 3D hot stretch-bending deformation behavior were studied.It was found that compared to the initial undeformed sample,TC4 titanium alloy undergoes uniaxial hot stretching deformation and 3D hot stretch-bending deformation,resulting in a decrease in the grain size of both phases,an increase inβphase content,and an increase in the density of geometrically necessary dislocations.Based on the theory of crystal plasticity and experimental results,a two-phase crystal plasticity model of TC4 titanium alloy was conducted to study its von Mises stress distribution and von Mises strain distribution under high-temperature uniaxial loading conditions,as well as the evolution law of two-phase dislocation density under different temperature loading conditions.It was found that as the temperature and strain increase,the von Mises stress distribution becomes more uniform.When the material undergoes deformation,the von Mises strain of theβphase is significantly higher than that of theαphase.Moreover,there is a significant difference in the evolution law of the two-phase dislocation densities during the deformation process.For theαphase,except for the basal and prismatic slip systems,the growth rate of dislocation density in other slip systems increases with increasing temperature.For theβphase,the growth rate of dislocation density decreases with increasing temperature. |
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