Effect of Zr+ ion irradiation on the mechanical anisotropy of Zr–2.5%Nb pressure tube material

Constant load pyramidal indentation creep tests were performed to study the effect of Zr+ ion irradiation on the anisotropy of the local plastic deformation of Zr–2.5%Nb pressure tube material at 25 °C. The ratio of the average indentation stress σ ind t = 0 on the transverse normal (TN) plane relative to that on the axial-normal (AN) and radial-normal (RN) planes is 1.3 and 1.2 respectively. After Zr+ ion irradiation the ratio of σ ind t = 0 on the TN plane relative to σ ind t = 0 on the AN and RN planes is 1.04 and 1.08 respectively indicating that the anisotropy of the yield stress is decreased as a result of irradiation hardening. The relative change in indentation stress Δ σ ˆ , as a result of irradiation damage, decreases with increasing resolved basal pole fraction in the indentation direction. This suggests that the Zr+ ion irradiation damage has a greater effect on blocking the movement of dislocations on prismatic slip systems compared to pyramidal slip systems in the Zr–2.5%Nb pressure tubing. The activation energy ΔG0 of the obstacles that limit the rate of dislocation glide during indentation creep at 25 °C does not change with indentation direction but does increase with increasing levels of Zr+ ion irradiation damage.