The microstructure evolution history and the underlying mechanism of an α/β dual phase titanium alloy during elastic-plastic deformation process

In this paper, in situ scanning electron microscope tensile test was carried out on the Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy, and the mechanism of grain rotation, shape change and micro-strain redistribution in macroscopic elastic deformation (stage I), macroscopic elastic-plastic transition (stage II) and macroscopic plastic deformation (stage III) stages were quantitatively investigated by electron backscatter diffraction and digital image correlation. In stage I, it was found that 10.1% of the viewing zone underwent grain rotation or shape change, and the micro-strain was mainly distributed in primary α phase (α_p) and their intersection. The result of the separately designed elastic loading-unloading tensile test showed that the rotated α_p no longer returned to the primary orientation. In stage II, the tensile plastic deformation regions reached 52.9%, and grains in β_T regions continued to rotate and began to change shape. In stage III, 84.6% of the viewing zone got into the tensile plastic deformation state. Combined with geometrically necessary dislocation density distribution, it was found that some of the regions in low strain state (0 ≤ ε<1%) actually underwent complex tensile plastic deformation. In addition, the maximum micro-strain of the viewing zone was transferred to β_T regions.