THERMAL AND DYNAMIC PARTITION OF DUMBBELL INTERSTITIALS IN COMPLEX CONCENTRATED ALLOYS AND LITERATURE SURVEY OF SOLUTE PRECIPITATION IN REACTOR PRESSURE VESSELS

Abstract

This thesis consists of two main parts.

Part I of this study focuses on thermal and dynamical partition of dumbbell interstitials in complex concentrated alloys (CCAs). The results have been published in Scripta Materialia (attached as Appendix B). CCAs are promising candidates for applications in extreme conditions, such as irradiation where interstitial mediated diffusion is important. In CCAs with 𝑁𝑁 principal elements,

𝑁𝑁(𝑁𝑁+1) 2

types of dumbbell interstitials exist. Currently, there is no way to predict the thermal partition (fractional concentration at equilibrium) and the dynamic partition (fractional time an interstitial spends during diffusion) of each type of dumbbell interstitial. To mitigate this issue, this work proposes a theoretical model for computing the equilibrium concentrations and thermal partition of dumbbell interstitials in CCAs and validates the model using grand canonical Monte Carlo simulations. Lattice kinetic Monte Carlo simulations show that the thermal partition is equivalent to the dynamic partition, and both are governed by composition and formation energies of dumbbells. The model proposed provides a fundamental piece for understanding radiation enhanced diffusion and induced segregation in CCAs under irradiation. Part II of this study focuses on literature surveys of solute precipitation in reactor pressure vessels (RPV) and is published as a part of review article on Journal of Nuclear Materials (attached as Appendix C). Irradiation-induced hardening and embrittlement in RPV steels have been identified as a primary concern for extending the lifetime of nuclear power plants. A large body of works indicate this phenomenon is related to solute precipitation in RPV, including Cu-rich precipitates (CRPs) and Mn/Ni-rich precipitates (MNPs). While great advancement has been achieved in the last few decades in understanding solute precipitation in RPV steels, predicting the precipitation over time in RPV steels under irradiation and the resulting hardening and embrittlement remains a challenge. Focusing on modeling perspectives, we review the key aspects of solute precipitation of RPV steels under irradiation and identify gaps in current understandings, as a part of a comprehensive review that serves to point out future research directions.