Multiscale Simulation Study On Superplasticity Deformation Of WSTi3515S Burn-resistant Titanium Alloy

WSTi3515S burn-resistant titanium al oy has good coarse-grained superplasticity under proper deformation conditions.The al oy has multi-scale effects during superplastic deformation: stress and strain at the macro level;evolution of the microstructure at the meso level;atom diffusion and dislocation motion at the micro level.This multi-scale effect can determine the mechanical properties of the al oy and reveal its deformation mechanism.At present,the research on the superplastic properties of WSTi3515 S burn-resistant titanium alloy mainly focuses on the experiment,and the good process parameters to obtain are determined by studying the deformation behavior and the evolution of microstructure.However,experimental studies cannot describe the dynamic evolution of deformation,and it is diffic ult to reveal the complex microscopic physical phenomena in the superplastic deformation process.Therefore,in this paper,the tensile deformation behavior of WSTi3515 S burn-resistant titanium al oy was simulated by establishing a multi-scale model,and deeply studies the superplastic deformation of the alloy.The research contents and results are as follows:The macroscopic mechanical response and mesoscopic stress distribution of WSTi3515 S al oy during superplastic deformation were analyzed.At the beginning of deformation,plastic flow in the center,where the flow stress rises rapidly.With the increase of strain,the flow stress at the center position was constrained by the stress at other positions,and develops from the center region to the periphery,and finally reached a certain balance to achieve unifo r m deformation.The deformation behavior of the al oy is greatly affected by temperature,strain rate and deformation amount.The higher the temperature,the lower the strain rate and the greater the amount of deformation,which makes the distribution of stress and strain more uniform.So that the deformation continues continuously and uniformly,so as to obtain better superplasticity.The effect and coordination of grain boundary in the overall deformation were studied.At the beginning of the deformation,the stress at the grain boundary is significantly greater than the internal stress of the grain,and the grain boundary tends to become a stress concentratio n area.As the deformation continues,the grain boundary area begins to soften until the grain boundary stress is completely less than the average unit stress inside the grain.Therefore,the deformation at the grain boundary is coordinated.During the entire deformation process,the equivalent plastic strain at the grain boundary is always greater than the strain in the crystal.As the deformation continues,the intragranular contribution to the deformation becomes more and more significant,indicating that the crystal boundary and intragranular participate in the deformation together.And different thicknesses of the grain boundary have different effects on the deformation.The relative thickness of the grain boundary increases,the force per unit grain boundary area is smal,and the strain difference between the grain boundary and the grain is smal,which promotes the coordinated deformation within the crystal is improved,thereby improving the overall deformation ability of the material.The change rule of grain size during superplastic tensile deformation of WSTi3515 S burnresistant titanium al oy were investigated.During the deformation process,the deformation of the grains is uniformly axisymmetric and regularly distributed.As the amount of deformatio n increases,the average grain size will change as the recrystal ized grains change,and the unit grain boundary area also changes.The increase of the unit grain boundary area makes the grain boundary participate in the coordinated deformation,which is more conducive to the superplastic deformation of the alloy.And increasing the deformation temperature and reducing the strain rate can promote dynamic recrystal ization,thereby enhancing the plastic deformatio n ability of the material.The deformation mechanism of the grain during simulation of the microstructure of the al oy is basically consistent with the experiment,so the microstruc t ure simulation of superplastic tensile deformation of WSTi3515 S burn-resistant titanium al oy have a certain reference value.