Thermoplastic Deformation Behavior And Numerical Simulation Of TA15Titanium Alloy At High Temperature

Titanium and titanium alloys are noted in astronautics and navigation applications fortheir relatively low density，non-magnetism，excellent corrosion resistance，highstrength-to-weight and strength-to-stiffness ratios. The formability of titanium alloys ispoor at room temperature, characterized by high deformation resistance. Plastic formingat elevated temperatures is the major process for manufacturing the titanium parts.Therefore, it has the practical significance to research the microstructure evolution andmesoscopic physical mechanism during the thermoplastic deformation of titanium alloyfor predicting material properties.Based on the experiments of isothermal compression on Gleeble-3500simulator, thehot deformation behavior and microstructure evolution of TA15titanium alloy underdifferent process parameters (temperature, strain rate and degree of deformation) wereinvestigated. The experimental results show that the main softening mechanism isdynamic recovery above β transition, the yield stress and peak stress decreasesobviously with deformation temperature increasing and stain rate decreasing, which alsoshow that titanium alloy is sensitive to strain and deformation temperature. The resultscould provide theoretical basis for the establishment of reasonable heat processingguideline and optimization of process parameters.In this dissertation, the mesoscopic physical mechanism and mechanical response ofTA15titanium alloy were researched by crystal plasticity finite element method duringthe thermoplastic deformation above β transition. The initial microstructure of TA15titanium alloy was established based on the cellular automaton and the orientation ofdifferent grains was chosen by the electron backscatter diffraction technique, Theinhomogeneity of deformation and mechanical response on mesoscale during hightemperature compression are simulated based on mechanisms of polycrystal dislocationmotion and plastic flow. The constitutive model incorporating both primary slip systemsand secondary slip systems is implemented to analyze the mechanical behaviour forbody centered cubic based on rate dependent crystal plasticity theory. The reasonableconstitutive parameters are established on the premise of the consistency ofexperimental and simulated stress-strain curves. The compressive simulations of TA15titanium alloy at high temperature are analyzed, including the stress and straindistribution, the activity of slip systems, the variation of grain area. The simulation results reveal that: the stress and strain distribution is inhomogeneous due to therandomness of grain geometry and orientation; the distribution of the stored energyagrees with the stress distribution and the energy could be evaluated quantitatively bydislocation theory; the activity of slip systems is different attributing to the complexintergranular interaction; the growth rate of grain boundary area increases withincreasing deformation degree and the grain density. The simulations provide atheoretical basis for solid phase transformation or microstructure evolution andmulti-scale synchronous coupled simulation.