Elucidating the mechanisms of gradient nanostructure on enhancing fatigue resistance of pure zirconium

In this paper, the strengthening mechanism and anti-fatigue mechanism of gradient nanostructure were discussed in detail, and a crack propagation rate model was established based on the characterization of gradient nanostructure and residual compressive stress. Results indicated that the gradient nanostructure exhibited several characteristics, including grain size, grain orientation, twin thickness/density, dislocation density gradient, and residual stress gradient. The strengthening effect mainly originates from nanograins/ultra-fined grains and twins. Compared with coarse-grained Zr (CG-Zr), the fatigue limit of gradient nanostructured Zr (GNS-Zr) was increased by about 25 %. The synergistic effect of gradient nanostructure and residual compressive stress enhances the resistance of crack initiation, effectively reducing the driving force and increasing the resistance of crack propagation, finally significantly improving the fatigue lifetime of GNS-Zr. A crack propagation rate model with gradient nanostructured characteristics was obtained.