Effects of grain size and initial immobile dislocation density on fatigue behavior of polycrystalline metals

Grain size and initial dislocation density introduced by different mechanical processing methods may have a strong influence on fatigue behavior of polycrystalline metals. Using the reaction-diffusion model developed by Walgraef and Aifantis, we examined the ability of fatigue dislocation patterning and the evolution of dislocation density in the materials with different grain sizes (100 nm-10 μm) and initial immobile dislocation densities (IIDD, 1×1012 m−2-1.58×1015 m−2). The results show that there is a clear relation among the necessary length scale for dislocation patterning, the grain size and the IIDD. Furthermore, the nominal life for fatigue damage initiation of these materials was evaluated based on the evolution of dislocation density and the ability of the dislocation patterning, showing good consistency with the experimental findings.