Microstructure characteristics of gradient nano-grained Ti-1300 titanium alloy induced by sliding friction treatment

A gradient nano-grained layer in Ti-1300 alloy is successfully fabricated by sliding friction treatment, and the microstructural characteristics and grain subdivision process are systemically investigated. The results show that uniform equiaxed beta grains with an average size of around 70 nm in the topmost surface are generated due to the ultra-high plastic strain. The microstructure near substrate consists of high density dislocations and deformation slip bands, while the different microstructures featured of dislocation tangles, dislocation walls and lamella shaped subgrains are closer to the surface. The rotation dynamic recrystallization is responsible for grain refinement of Ti-1300 alloy. Moreover, the gradient nano-grained sample with the high strength properties possesses a high level of ductility in comparing to the initial coarse-grained one. The strain hardening behavior and grain refinement are considered as the main strengthening mechanism, and the high ductility is mainly attributed to the specific deformation mechanism for gradient nano-grained microstructure.