LAUSR

ABSTRACT The uniaxial flow stress of 1 μm diameter micro-pillars made from single α Zr grains cut from Zr–2.5%Nb CANDU pressure tube material was assessed in the non-implanted condition and after 6.0 dpa Zr+ implantation performed at 25°C and 300°C to simulate neutron irradiation. The normal flow stress, at 10% strain, of the non-implanted micro-pillars was about 70% higher than that for larger diameter polycrystalline pillars indicating length-scale dependence. The flow stress anisotropy displays a stronger length-scale dependence for micro-pillars that were loaded along the <0001> basal pole direction than along other directions. The normalised shear stress of α Zr micro-pillars aligned for single-slip deformation displayed a dependence upon crystal orientation. These findings provide new information on the mechanisms by which small volume α Zr phase ligaments, located in crack-tip regions, deform plastically and thus contribute to the ductile fracture toughness of neutron-irradiated Zr–2.5%Nb CANDU pressure tubes.