3D Complex Microstructure Model Construction And Static/Dynamic Mechanical Behavior Simulation Of TC6 Titanium Alloy

Titanium alloy has many excellent properties such as low density,high strength,good heat resistance and corrosion resistance,but its static / dynamic mechanical properties are very sensitive to microstructure.Besides,the microstructure features exhibit a different complex characteristics such as phase size,phase morphology and phase distribution under the different heat treatment process parameters,thus making it very difficult to precisely control the mechanical properties of titanium alloy.The quantitative relationship between microstructure characteristics and mechanical properties is established by numerical simulation method,which is very important for revealing the mechanical response process and internal mechanism of the material and optimizing the process parameters.However,the numerical simulation method based on the traditional two-dimensional microstructure does not reflect adequately the complex microstructure distribution characteristics of the titanium alloy in three-dimensional space,which greatly affects the reliability of the calculation results.Therefore,the typical TC6 titanium alloy is used to investigate its complex microstructure 3D model construction and static / dynamic mechanical behavior simulation with a systematic and in-depth study.In order to provide a reliable technical support for carrying out mechanical behaviors simulation of TC6 titanium alloy based on 3D microstructure,five simple,efficient and professional software were developed by using Python advanced programming language based on ANSYS / LS-DYNA large commercial finite element software.Related software is as follows:(1)Microstructure-based Finite Element Model Construction Software(MF),which simplifies the complicated construction process of microstructure finite element model and ensures the mesh size uniform.(2)Bilinear Constitutive Parameters Determination Software Based on Nanoindentation Test(BCN),which solves the difficulty to determine the single-phase quasi-static mechanical constitutive parameters.(3)Microstructure-based Finite Element Simulation Softw(MFES),which simplifies the complicated finite element solving process.(4)Dynamic Mechanical Constitutive Parameters Verification Software(DMCPV),which effectively improves the reliability of the dynamic constitutive parameters of the material.(5)Macro-micro Coupling for Multi-scale Simulation Software(MCMS),which can effectively calculate the micro-mechanical response behaviors in the local region of macroscopic structural parts.The 3D complex microstructure model construction,quantitative characterization and finite element meshing of TC6 titanium alloy were realized.The dual-energy micro-computed tomography(Micro-CT)imaging was employed to overcome the difficulty of low absorption contrast since there is no significant difference in density among the primary ? phase,secondary ? phase,and ? phase of TC6 titanium alloy.The 3D microstructure model of TC6 titanium alloy was first achieved by laboratory X-ray microtomography,and then analyzed quantitatively.It is found that the volume fractions of the primary ? phase,secondary ? phase and ? phase are 28.32%,47.78% and 23.90%,respectively.Some complex microstructural features of TC6 titanium alloy such as spatial distribution,shapes,and interconnectivities were also successfully captured.In 3D space,the primary ? phase is composed of discrete equiaxed grains and interconnected grains,and the fraction of the individual equiaxed grains is up to 50%;the secondary ? phase interconnects with ? phase forming a completely interconnected network.The 3D phase structure finite element mesh model was successfully achieved by mapping the image pixels and the elements of the finite element model.Then,the 3D grain structure finite element mesh model which reflects the crystal orientation information was also obtained by employing a mesh random segmentation algorithm.A new in-depth evaluation of the internal stress / strain evolution in 3D space,and the influence of microstructure on the elastic-plastic deformation process of TC6 titanium alloy subjected to uniaxial tensile loading was performed based on the 3D microstructure finite element mesh model.Constitutive relations of the constituent phases were determined via synchrotron-based in-situ high-energy X-ray diffraction and a self-consistent model as well as nanoindentation tests combined with finite element modeling.The results revealed that the stress concentration was translated from the primary ? phase to the secondary ? phase,then to the ? phase in the elastic-plastic transition stage,while the plastic strain was always concentrated in the primary ? phase.As the deformation continues,the stress concentration was re-transferred to the primary ? phase while the plastic strain is concentrated at the interface of the primary ? phase,which might lead to the initiation of microcracks.In addition,the quasi-static tensile simulation results based on 3D grain structure show that the grain orientation has a significant effect on the equivalent stress concentration inside the model.The equivalent stress peak first appears in the grains with the equivalent modulus in the loading direction.Based on the proposed macro-micro multi-scale simulation method,the adiabatic shear deformation process of the local region in macro cylindrical dynamic compression specimen(?5 mm × 5 mm)of TC6 titanium alloy was simulated,and the microstructure evolution process and internal mechanism subjected to complex stress state with high strain rate was also revealed.By extracting the load information in the adiabatic shear zone of the macroscopic specimen and applying it to the 3D microstructure model,the multi-scale simulation was carried out.It is found that the mechanical behavior of each phase is significant before the macro bearing stress collapse: ? has the highest contribution to the overall strength of the material,while primary ? phase contributes the most to the plasticity.After the macro bearing stress collapse,the mechanical properties difference of the three phases in the adiabatic shear zone disappeared rapidly,and the final shear band width was 5?m,which is consistent with the SEM observation results.The temperature field distribution in the shear zone was obtained by thermodynamic coupling calculation.It is found that the temperature in the adiabatic shear zone reaches about 780 ?,which exceeds the recrystallization temperature(680 ?)of TC6 titanium alloy,providing the power for microstructure dynamic recrystallization.