Texture evolution and controlling of high-strength titanium alloy tube in cold pilgering for properties tailoring

As one of the preferred fabrication technologies for high-strength titanium alloy tubes, cold pilgering has unique advantages of large deformation, fine surface, and close dimensional tolerance since materials are incrementally experiencing compressive stress states dominated local loading throughout entire rolling process. However, both complex external loading history and low symmetric hexagonal close-packed (HCP) crystal structure induce heavy crystallographic reorientation of polycrystalline significantly influencing formability and performance of titanium tubular products. How to achieve a bespoken tailoring of texture related properties is still a challenge. Accordingly, taking high-strength Ti-3Al-2.5 V tubes as the case material, this study focuses on the tube texture evolution and the texture controlling guidelines for properties tailoring in cold pilgering. By coupling validated and verified three dimensional finite element (3D-FE) model and viscoplastic self-consistent (VPSC) crystal plasticity model, a macro-meso scaled computation platform is established to predict the inhomogeneous deformation flow and texture evolution during pilgering. Then the tube texture evolution characteristics along rolling process with three typical initial textures are investigated, and the correlation between texture evolution and spatial inhomogeneous deformation allocation is explored, in which the deformation history is fully featured by strain vector, viz., strain ratio α and equivalent plastic strain ε_e as well as ratios of wall thickness thinning to outer diameter reduction (total Q value and transient Q value). Taking the contractile strain ratio (CSR) as the most important indicator for evaluating the texture and properties, the effect of final texture features of the tube on its tensile mechanical properties is revealed, and then the texture controlling guidelines for properties tailoring of the tube are proposed. To obtain the desired near radial texture and the reasonable CSR, the different pass rolling specifications can be considerably designed to coordinate the spatial strain components based on reasonable range of total Q value and ε_e, then the rolling tools can be designed for further fine tuning of the transient Q value and strain ratio α.