Deformation Anisotropy of Annealed Zircaloy-2 as a Function of Fast Neutron Fluence

For unirradiated Zircaloys, plastic deformation occurs mostly by < a >-type dislocation glide on prismatic planes. The critical resolved shear stress of the prismatic slip system is lower than that of the other deformation systems (< a > slip on basal planes, and < a > or < c+a > slip on pyramidal planes, and twinning). This means that the yield strength (and ultimate tensile strength) for directions with a strong basal pole texture is higher than directions with a strong prism pole texture. Irradiation increases the yield stress on all slip planes due to the formation of dislocation loops that act as barriers to slip. Experimental evidence from Zircaloy-2 samples irradiated at 70 degrees C suggests that the increase in critical resolved yield stress due to irradiation is lower for basal compared with prism planes.