"A kinetic lattice Monte Carlo study of post-irradiation annealing of model reactor pressure vessel steels"
G. Robert Odette, Shipeng Shu, Peter Wells, Dane Morgan,
Journal of Nuclear Materials
Significant embrittlement in reactor pressure vessel (RPV) steels can be caused by the formation of nanometer-scale MneNieSi precipitates (MNSPs) and annealing is a promising technique for reducing embrittlement. To achieve better understanding of the evolution of these precipitates at the atomic scale, a kinetic lattice Monte Carlo (KLMC) model, parameterized using CALPHAD and recent atom probe tomography (APT) data, is used to simulate post-irradiation annealing of MNSPs. The model predicts MNSP volume fractions, number densities and sizes that agree well with the experimental observations. The model also predicts that the initial structure of the precipitates may be B2 bcc phases with one sublattice occupied by Ni and the other sublattice occupied by Mn and Si, as well as shows a modest temperature dependence of the MNSP composition. The results show that the simple approach can be used to model MNSP evolution and supports that these precipitates are stable thermodynamic phases.
|"CuMnNiSi precipitate evolution in irradiated reactor pressure vessel steels: Integrated Cluster Dynamics and experiments" Mahmood Mamivand, Peter Wells, Huibin Ke, G. Robert Odette, Dane Morgan, Acta Maerialia Vol. 180 2019 199-217|
|"Evolution of small defect clusters in ion-irradiated 3C-SiC: Combined cluster dynamics modeling and experimental study" Cheng Liu, Li He, Yizhang Zhai, Beata Tyburska-Puschel, Paul Voyles, Kumar Sridharan, Dane Morgan, Izabela Szlufarska, Acta Materialia Vol. 125 2017 377-389 Link|
|"Radiation-induced mobility of small defect clusters in covalent materials" Hao Jiang, Li He, Dane Morgan, Paul Voyles, Izabela Szlufarska, Physical Review B Vol. 94 2016 024107 Link|
"Thermodynamic and kinetic modeling of Mn-Ni-Si precipitates in low-Cu reactor pressure vessel steels"
Nathan Almirall, Philip Edmondson, G. Robert Odette, Peter Wells, Huibin Ke, Leland Barnard, Dane Morgan,
Formation of large volume fractions of Mn-Ni-Si precipitates (MNSPs) causes excess irradiation embrittlement of reactor pressure vessel (RPV) steels at high, extended-life fluences. Thus, a new and unique, semi-empirical cluster dynamics model was developed to study the evolution of MNSPs in low-Cu RPV steels. The model is based on CALPHAD thermodynamics and radiation enhanced diffusion kinetics. The thermodynamics dictates the compositional and temperature dependence of the free energy reductions that drive precipitation. The model treats both homogeneous and heterogeneous nucleation, where the latter occurs on cascade damage, like dislocation loops. The model has only four adjustable parameters that were fit to an atom probe tomography (APT) database. The model predictions are in semi-quantitative agreement with systematic Mn, Ni and Si composition variations in alloys characterized by APT, including a sensitivity to local tip-to-tip variations even in the same steel. The model predicts that heterogeneous nucleation plays a critical role in MNSP formation in lower alloy Ni contents. Single variable assessments of compositional effects show that Ni plays a dominant role, while even small variations in irradiation temperature can have a large effect on the MNSP evolution. Within typical RPV steel ranges, Mn and Si have smaller effects. The delayed but then rapid growth of MNSPs to large volume fractions at high fluence is well predicted by the model. For purposes of illustration, the effect of MNSPs on transition temperature shifts are presented based on well-established microstructure-property and property-property models.
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