Hot Deformation Behavior And Process Optimization Of TC4 ELI Titanium Alloy ?+? Region

In this paper,the ultra low clearance of titanium alloy TC4 ELI with lower impurity content as the research object,using the isothermal constant strain rate compression tests,the more in-depth research on deformation temperature750?~950? and strain rate of 0.001s-1~70s-1hot deformation behavior and microstructure evolution of the construction,which can accurately describe the constitutive relationship model of mechanical behavior of titanium alloy TC4 ELI during hot compression,and the processing parameters were optimized by processing map technology.From the titanium alloy TC4 ELI true stress-strain curve analysis we can know,the sensitivity of deformation temperature and strain rate on the flow stress is high,and the deformation temperature decreased with the increase of strain rate,the flow stress is decreased;in the initial stage of deformation,the alloy flow stress increases rapidly with the increase of strain in the small strain,the flow stress reaches the peak,then the alloy flow stress decreases,the flow stress increases with strain decreased to a certain extent will tend to ease.Through the observation of the microstructure of titanium alloy TC4 ELI,it is shown that,with the decrease of strain rate,the equiaxed fine grains of ? lamellae are changed,and the dynamic recrystallization is more abundant.The strain rate is decreased to 0.01s-1,the ? lamellae disappeared,equiaxed grains are uniformly distributed;at the same strain rate under the premise,as the temperature increase,?lamellae balling phenomenon is more significant,more conducive to the process of dynamic recrystallization.When the deformation temperature increases to titanium alloy TC4 ELI,the microstructure of the alloy will undergo phase transition and a large number of lamellar structure.Respectively using Arrhenius equation,multiple linear regression model and BP artificial neural network model in three ways to construct the constitutive relation model of titanium alloy TC4 ELI,the average error is 17.51%,7.63% and 1.36%respectively,which shows that the BP artificial neural network model has high accuracy and is suitable for the numerical simulation of flow stress of titanium alloy TC4 ELI.Based on the material dynamic model and Prasad criterion,and the isothermalconstant strain compression test data,the processing map of TC4 titanium alloy under different strain is established.Combined with microstructure observation,microstructure mechanisms of titanium alloy TC4 ELI in instability region were analyzed.The results showed that adiabatic shearing and flow localization behavior tend occurred at the rang of temperature from 800? to 875? and stain rate form0.1s-1 to 10s-1,the region is a flow instability zone,which should be avoided in the hot working process.Based on the different processing map variables under analysis and combined with the verification of the microstructure,determine the best thermal deformation range of thermodynamic parameters are: the deformation temperature range of840~950?,the strain rate range of 0.001~0.01 s-1;the better the thermal deformation of the thermodynamic parameters are: the deformation temperature range of750~840?,the strain rate range of 0.001~0.003 s-1.The deformation mechanism of the region is dynamic recrystallization,which is a good thermal processing parameter for titanium alloy TC4 ELI.