Strain transfer behavior and crystallographic mechanism of crack initiation during cyclic deformation in zirconium

Abstract

Fully-reversed cyclic deformation of a pure Zr (a thickness of 17 mm) was conducted at two different strain amplitudes (0.4% and 0.8%) to investigate the deformation and crack initiation behaviors based on slip trace analysis. It was found that prismatic 〈a〉 slip with a higher Schmid Factor (m > 0.4) was the dominant deformation mode. The grains containing persistent slip bands (PSBs) tended to go towards [1¯21¯0] pole and the Schmid Factor had a critical value of 0.4 above which prismatic and pyramidal slip were dominant. Fatigue cracks were mainly initiated at PSBs and grain boundaries (GBs). It showed that 61.1% of the cracks were PSB cracks under a strain amplitude of 0.4%, while it decreased to 53.5% at a strain amplitude of 0.8%. PSB cracks were mainly parallel to prismatic 〈a〉 slip with higher Schmid Factor while some cracks tended to be initiated at GBs with higher misorientation angles. The interaction of PSBs with GBs would result in strain transferring to the neighboring grain. Strain transfer was more likely to occur at the condition of the higher geometrical compatibility factor m′, and lower residual Burgers vector Δb, which could reduce strain localization.