Atomistic Simulation of Radiation-induced Defects in Ni-based Systems

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Ferasat, Keyvan
Atomistic simulations , Ni-based alloys
Nickel (Ni)-based alloys show outstanding mechanical and physical properties at high temperatures and in corrosive environments. Therefore, Ni with measured additions of appropriate alloying elements would be a good structural material candidate for the next generation of nuclear reactors. One such example of particular interest in Canada deuterium uranium (CANDU) reactors is X-750 Ni-based spacer material, which is a modified 600 series alloy, strengthened by the addition of aluminum (Al) and titanium (Ti). However, such Ni and Ni-based alloys, when exposed to radiation under working conditions, form defects which ultimately degrade their mechanical properties. This dissertation addresses several questions with regards to point defect evolution in Ni and Ni-based alloys by employing atomistic scale modelling in order to understand and predict alloy performance in irradiated environments. Presented in this manuscript format, the dissertation can be outlined as follows: all utilized atomistic techniques in this thesis are explained in Chapter 2. Chapter 3 identifies the role of self interstitial atoms (SIAs) in the re-ordering of disordered Ni3Al, and moreover an applicable model for mean-field rate-theories is also presented. Chapter 4 indicates the complexity of energy landscape on point defect diffusion and localized traps in Ni(x)Fe(1−x) (0 ≤ x ≤ 1) using an in-home AkMC code. A modified version of this code is used to study point defect transport properties in Ni-Fe-Cr ternary alloy systems (appendix A). Helium (He) bubble evolution in pure Ni system as a model for Ni-based alloys is studied and the role of different objects on bubble growth are discussed in Chapter 5. In the final chapter, the primary conclusions of these studies and future steps are explored.
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