Orientation dependent evolution of plasticity of irradiated Zr-2.5Nb pressure tube alloy studied by nanoindentation and finite element modeling

Abstract

The effect of heavy ion or neutron irradiation on the plasticity of Zr-2.5Nb pressure tube alloy is investigated by a combination of nanoindentation and numerical modeling, with indentation tests along the tube axial (AD) and transverse directions (TD). The true stress-strain curves are calculated from nanoindentation load-displacement curves based on an analytical model. The work hardening behaviors of samples loaded in different orientations are compared before and after irradiation. Heavy ion irradiation up to 1.2 × 1015 ion/cm2 significantly increases the hardness of both AD and TD samples. The analytical model can precisely capture the plastic properties of both unirradiated and irradiated material. The calculated true stress-strain curves, including elasticity, yield strengths, and work hardening behaviors of unirradiated and irradiated samples show reasonably good agreement with experimental stress-strain curves derived from uniaxial tensile tests. The change of work hardening exponent due to irradiation shows strong orientation dependency; it decreases from 0.22 to 0.11 in AD but stays almost the same at ∼0.09 in TD after ion irradiation. The work hardening exponent is about 0.16 and 0.08 for neutron irradiation AD and TD samples, respectively. These orientational differences are related to the anisotropic interactions between plastic-flow dislocations and irradiation induced prismatic <a> dislocation loops.