Research On Microstructure Evolution And Mechanical Properties Of TC4 Titanium Alloy Under Different Heat Deformation Conditions

The TC4 titanium alloy has been widely used in industrial sectors such as aviation,marine,and automotive due to its exceptional mechanical properties.However,titanium alloys exhibit strong resistance to deformation and high resilience at room temperature,making TC4 titanium alloy plates usually formed at high temperatures.During hot working processes,the microstructure and properties of material are significantly affected by deformation parameters.In order to improve the usability of TC4 titanium alloy in practical production processes,this study investigates the effects of different deformation conditions（deformation temperature,strain rate,heating temperature,heating rate）on the flow behavior,microstructure evolution,and mechanical properties of the alloy during its hot plastic deformation process,based on high-temperature tensile testing,high-temperature compression testing,and hot stamping experiments.Additionally,a new technology-the fast hot stamping process was adopted to widen the processing window of the hot stamping forming of the TC4 titanium alloy,improving the formability and efficiency of the alloy.（1）The traditional uniaxial hot tensile tests were carried out on TC4 titanium alloy sheets within the strain rate range of 0.01～5 s^-1 and the temperature range of 800～950℃.The effects of deformation temperature and strain rate on the high temperature rheological stress and mechanical properties of TC4 titanium alloy were explained.In addition,the microstructure and fracture morphology of the deformed material were examined to determine the microstructure evolution law and high-temperature damage evolution mechanism of TC4 titanium alloy under large deformation conditions.Finally,the suitable processing window for TC4 titanium alloy was determined to be at 850～900℃and a strain rate of 0.01～0.1 s^-1.（2）To reduce the material’s dynamic softening at high strain rates,a graded quenching process from 950℃→800℃was designed.Compared with the traditional hot tensile forming process at 800℃,the elongation of the material was improved,the strain softening of the material was diminished,and its strain rate hardening efficacy was enhanced.（3）Single-axis tensile tests were conducted on TC4 titanium alloy with fast/slow heating at temperatures ranging from 850～950℃on the basis of the graded quenching process to investigate the effect of heating rate and temperature on the formability and post-forming hardness of the alloy.（4）In order to study the thermal deformation constitutive model of TC4 titanium alloy,high-temperature compression tests were carried out under the same conditions as traditional hot tensile testing.The obtained stress-strain curves were corrected for temperature rise and friction,and the modified-Johnson Cook model,Arrhenius model,and Laasraoui segmented model were established using plastic section data to accurately describe and predict the material’s high-temperature flow behavior.（5）The U-shaped workpiece hot stamping experiments were conducted at different heating temperatures（600～950℃）.It was found that when using traditional hot stamping technology,the processing window was very narrow,and qualified parts could only be obtained within the heating temperature range of 750～850℃,and the forming efficiency of the entire process was low.Microstructure analysis of the large deformation area of the U-shaped workpiece revealed that the decrease in formability was caused by phase transformation,grain coarsening,and oxidation during prolonged heating and insulation processes.To solve this problem,a fast hot stamping process was proposed:the heating rate was increased to 100℃/s,and the sample was immediately hot deformed after being rapidly heated to the specified temperature.It was found that qualified parts could be formed at temperatures ranging from 850℃to 950℃.Therefore,the fast hot stamping process can improve the forming efficiency and expand the temperature window of TC4 titanium alloy hot stamping to 950℃.In addition,through microstructure analysis and hardness tests,the optimal forming temperature under fast hot stamping process was determined to be 900℃,which can ensure the best plastic formability of the material and maintain a similar hardness to the initial material after forming.The study of key technologies provides a scientific basis for the selection of processing technology and parameters in actual production,achieving the goal of cost savings and efficiency improvement.