Microstructure evolution and mechanical properties of Ti-2Al-2.5Zr alloy tubes during multi-pass cold rolling

This work systematically investigates the microstructure evolution, texture transformation, deformation mechanism, and tensile response of Ti-2Al-2.5Zr tubes during multi-pass cold rolling using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and in-situ tensile testing. The novelty of this study lies in correlating rolling-pass-dependent microstructure and texture evolution with cooperative slip/twinning deformation behavior and mechanical property changes in small-diameter thick-walled titanium alloy tubes. With increasing rolling passes, the α-grain morphology evolves from relatively equiaxed to elongated/fragmented bands, accompanied by an overall refinement of the α microstructure. The Schmid-factor analysis indicates an enhanced tendency for prismatic slip, whereas basal slip remains nearly unchanged, and a small amount of {10-12} tensile twinning is observed to assist local strain accommodation. Meanwhile, the maximum α-texture intensity shows an overall decrease at high deformation. Tensile testing demonstrates a clear strengthening effect: yield strength (YS) increases from 453.7 MPa to 562.1 MPa, and ultimate tensile strength (UTS) increases from 686.9 MPa to 755.1 MPa, while the ductility exhibits a slight reduction. These results reveal that strengthening is mainly associated with dislocation accumulation and microstructure refinement, whereas the retained ductility is related to coordinated slip/twinning deformation and texture dispersion.