Crystal Plasticity Finite Element Method Simulation Of Plastic Behavior Of Ti₃Al Single Crystal And Dual-Phase Lamellar TiAl Alloy

Crystal plasticity finite element method（CPFEM） is a model that incorporates the crystal plasticity theory into the framework of finite element method. The crystal plasticity constitutive law in the model is based on dislocation slips, deformation twin and lattice distortion. So it can give an essential description on the material plastic deformation compared to macroscopically isotropic constitutive law. In this paper, CPFEM simulations were carried out by commercial FEM software of ABAQUS. It was mainly studied on the activation of slip systems in Ti₃Al single crystal with different orientation, and the influence of prismatic and basal slip system on the yield stress of dual-phase lamellar TiAl alloy. The main contents are as follows:（1） Crystal plasticity constitutive law subroutines for Ti₃Al phase and dual-phase lamellar TiAl alloy were established based on dislocation slip and twining deformation mechanism within the frame of crystal plasticity theory. Then, the corresponding subroutines were used to simulate the plastic deformation of Ti₃Al single crystal and dual-phase lamellar TiAl alloy.（2） The simulation results of unidirectional compression of Ti₃Al single crystal show that basal slip of（0001）<1120>, prismatic slip of {1010}<1120>, and pyramidal slip of {1121}<1126> can be activated during the plastic deformation. However, there are dramatic differences on the ease or complexity of activation of various slip systems, which is due to the difference of critical shearing stress and schmid factor. It is difficult for basal slip and pyramidal slip to be activated because of their larger critical shearing stress, which leads that the activation of basal slip and pyramidal slip just occurs with larger schmid factor. Pyramidal slip systems only can be initiated when compression axis is close to [0001] direction due to the maximum shearing critical shearing stress, especially. Prismatic slip is easier to be activated and also has the largest contribution to the plastic deformation.（3） A microstructural model for dual-phase lamellar TiAl alloy containing true twin crystal, pseudo twin crystal, 120°rotational order-fault and two types of phase boundary of γ/α has been established. The simulation results of unidirectional compression reflect strong plasticity anisotropic behavior. The lamellar orientation has dramatic effect on the stress-strain behavior of dual-phase TiAl alloy. The yield stress is the maximum at the lamellar angle of 90°and the minimum at the lamellar angle of 45°. Furthermore, the yield stress value of simulation has a good agreement with the experimental data.（4） Prismatic slip system of Ti₃Al has effect on the yield stress of dual-phase lamellar TiAl alloy with lamellar angle between 0°and 20°during the plastic deformation of dual-phase lamellar TiAl alloy. Basal slip system has no effect on the yield stress.（5） With the tension simulated at the lamellar angle of 0°, the interface structural difference of the true twin crystal, pseudo twin crystal and 120°rotational order-fault leads to dramatic difference on the active sequence and the slipping evolution of the slip systems and twinning systems, even with the same Schmid factor during the deformation of dual-phase lamellar TiAl alloy.