Deformation microstructures of non-irradiated and proton irradiated zirconium alloy from nanoindentation creep tests characterised by TEM

Indentation creep tests were conducted on non-irradiated and proton irradiated Zircaloy-2 at different temperatures. After indentation creep testing, areas beneath the indentation tip were lift-out by (Focused Ion Beam) FIB, then deformation microstructures of the plastic zone were characterized by TEM. We observed that although it has the highest critical resolved shear stress of available slip modes during room temperature plasticity, under creep deformation < c + a > dislocations play a significant role in the indentation deformation process. These edge < c + a > dislocations form dipoles that impede dislocation motion and cause work hardening. For non-irradiated samples, < c + a > dislocation density in samples tested at 300 degrees C is significantly lower than those tested at room temperature. This may be due to the formation of {1101} <1012> twins at 300 degrees C, which is observed in both irradiated and non-irradiated samples. However, there is no decrease in < c + a > dislocation density at high temperature in irradiated samples. This is hypothesised to be because irradiation induced loops have more effect in impeding the motion of < a > type dislocations than < c + a > dislocations. In addition, annealing of < c + a > dislocation dipoles at 300 degrees C during creep of the non-irradiated sample may contribute to the decrease in < c + a > dislocation density. Irradiation induced < a > loops were swept away by gliding < a > dislocations during indentation deformation. Irradiation loops that were close to the indent were significantly eliminated while loop-free channels that were parallel with the basal trace formed at positions further away from the indent.