## 1 Introduction
[21] studied micro slip activation and localization in Ti-6 Al-4V quantitatively using high-resolution digital image correlation (HR-DIC), HR- EBSD and crystal plasticity finite element modeling, finding the texture beneath the characterized free-surface can affect the local slip, stress distribution, lattice curvature, and GND density. Progress has also been made in the numerical simulation of complex interactions of polyphase systems. [PERSON] et al. [22] developed a duplex phase bimetal CPFEM model of Cu-Nb multilayer composites, which was compared with a multicrystal model. The results showed that co-deformation constraints imposed by the bimetal interfaces are strong, while those by neighboring grain boundaries are relatively weak. Some researchers have adopted a method of representative volume element (RVE). For instance, [PERSON] et al. [23] studied the stress-strain relationship between the ferrite and martensite phases in the commercial duplex DP980 steel and determined the microscopic hardening parameters for each phase by the CPFEM based on the RVE. The parameters successfully captured the influence of the crystallographic orientation of the ferrite phase on the localization of shear strain during uniaxial tension. [PERSON] et al. [24] employed a 2D RVE of duplex DP600 steel on the basis of a real microstructure. The authors successfully simulated the failure behavior of the steel and quantitatively described the interrelation between ductile damage in ferrite and the cleavage fracture of martensite under multi-axial loading conditions. In addition, the method of cellular automata (CA) was adopted. For example, [PERSON] et al. [25] developed a CA model with which both virtual and real microstructures can be generated or imported into, and successfully simulated the grain growth of a single phase material (austenitic stainless steel 304L) and a dual phase-material (Ti-6 Al-4V). [PERSON] et al. [26] presented a CA model to predict the morphological evolution, average grain size, topological characteristics and the coarsening kinetics of the TA15 alloy during static coarsening and found that the predicted coarsening kinetic constant increased with the volume fraction of the \(\alpha\) phase and that a larger initial grain size led to slower coarsening. Although some research on the modeling of polyphase materials and the interphase interactions has made progress, some deficiencies still exist. For example, in view of the simulation of slip band evolution, [PERSON] et al. [18; 21] adopted a duplex titanium model; however, the authors analyzed the slip evolution of the \(\alpha\) phase while the analysis of the \(\beta\) phase was lacking. Furthermore, for the relationship between slip system activation and the SFs, they reported a phenomenon where the basal slip system activation occurs preferentially with lower SFs [10]. However, their work lacked further discussion and quantitative analysis. In addition, for the grain interactions, [PERSON] et al. [21] found the initial inter-granular misorientations greater than about 5\({}^{\circ}\) can influence the subsequent micromechanical grain behavior including slip, lattice rotation and GND density. However, in this study, the initial misorientation was measured by EBSD and the data during the deformation process was lacked. In addition, the author proposed a single-phase model, which resulted in the impossibility of analyzing the grain interactions of different phases. In this study, which was based on in-situ tensile testing of duplex titanium (Ti- 5 Al-2.5 Cr-0.5 Fe -4.5 Mo-1 Sn-2 Zr-3 Zn), a CPFEM model, which was based on a realistic microstructure image, has been developed to investigate the activation of slip systems in the \(\alpha\) and \(\beta\) phases, as well as the correlation between the grain interactions and slip system evolution during the plastic deformation at room temperature. In addition, we addressed the problem of slip system evolution in duplex titanium alloys.