| Popis: |
Accelerated irradiation studies in nuclear structural materials are essential for the roll-out of future GEN IV reactors. Over the operational lifetime of these systems, the associated embrittlement and hardening induced through neutron irradiation can be emulated through accelerator-based ion irradiation. While the complementarity of ion and neutron irradiation is evident, this thesis looks at the effects of the highly stratified damage profiles resulting from ion irradiation. Small scale experimental techniques, such as micro-tensile testing and nanoindentation, allow for the analysis of the shallow irradiation zones. A significant challenge to these techniques is the presence of gradient plasticity phenomena, that is most pronounced at these very shallow depths. Indenter size effects in nanoindentation can skew experimental results significantly. In addition, Hall-Petch type behaviour (grain size effects), along with strain rate sensitivity, will often affect the precision of micro-tensile test results. One of the major hypotheses underpinning the thesis is that ion-induced irradiation hardening is equivalent to Orowan-type strengthening. Suitable homogenisation techniques were adopted in light of the complementarity between the neutron and ion irradiation response. Validation of the hypotheses was through a systematic study of low and high dpa (displacements per atom) irradiation responses in a range of materials including austenitic stainless steel, single crystal nickel, duplex steel and a commercial aluminium alloy, with the aim of developing a synergetic and multiscale assessment framework. Kinetic Monte Carlo simulations of ion irradiation were used to inform a number of mesoscale and crystal plasticity finite element models and to better elucidate the gradient damage effects induced by ion irradiation. The multiscale simulations provided an accurate prediction of the hardness increase with a tractable pathway between the microscale testing and the mesoscale engineering response. Explicit and phenomenological treatment of the irradiation defects were shown to be commensurate, with a similar calculated rise in the critical resolved shear stress within the developed framework. |
