The Woodruff School

SUMMARY

The overall purpose of this dissertation is to develop a multi-scale framework that can simulate radiation defect accumulation across a broad range of time and length scales in metals. In order to accurately describe defect accumulation in heterogeneous microstructures and under complex irradiation conditions, simulation methods are needed that can explicitly account for the effect of non-homogeneous microstructures on damage accumulation. In this dissertation, an advanced simulation tool called spatially resolved stochastic cluster dynamics (SRSCD) is developed. The performance of the SRSCD framework is assessed by comparison to other simulation methods such as cluster dynamics and object kinetic Monte Carlo and experimental results including helium desorption from thin films and defect accumulation in neutron-irradiated bulk iron. SRSCD is next used to investigate radiation damage in three main types of microstructures, using iron as a test material: iron thin films, coarse-grained bulk iron, and nanocrystalline iron. Finally, the methodology developed in this dissertation is applied in the context of multi-scale modeling and experimental design. The impact of radiation damage on hardening of irradiated materials is investigated by using the results of SRSCD as inputs into polycrystalline crystal plasticity simulations. In addition, the temperature shift required to achieve equivalent damage accumulation during irradiation at different dose rates, such as in the case of using ion irradiation as a proxy for neutron damage. The scientific developments presented in this dissertation represent significant improvements over the state of the art due to improved simulations of defect accumulation and direct upscaling of results into polycrystalline plasticity models. The tools and understanding of defect behavior developed here will allow predictive modeling of metal degradation in reactor-relevant damage environments, including the defected microstructure and macroscopic material property changes due to irradiation.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Aaron Dunn

TIME:	Thursday, February 25, 2016, 2:30 p.m.

PLACE:	MARC Building, 201

TITLE:	Radiation damage accumulation and associated mechanical hardening in thin films and bulk materials

COMMITTEE:	Dr. Laurent Capolungo, Chair (ME) Dr. David McDowell (ME) Dr. Naresh Thadhani (MSE) Dr. Chaitanya Deo (ME) Dr. Rémi Dingreville (SNL) Dr. Enrique Martínez-Saez (LANL)

SUMMARY The overall purpose of this dissertation is to develop a multi-scale framework that can simulate radiation defect accumulation across a broad range of time and length scales in metals. In order to accurately describe defect accumulation in heterogeneous microstructures and under complex irradiation conditions, simulation methods are needed that can explicitly account for the effect of non-homogeneous microstructures on damage accumulation. In this dissertation, an advanced simulation tool called spatially resolved stochastic cluster dynamics (SRSCD) is developed. The performance of the SRSCD framework is assessed by comparison to other simulation methods such as cluster dynamics and object kinetic Monte Carlo and experimental results including helium desorption from thin films and defect accumulation in neutron-irradiated bulk iron. SRSCD is next used to investigate radiation damage in three main types of microstructures, using iron as a test material: iron thin films, coarse-grained bulk iron, and nanocrystalline iron. Finally, the methodology developed in this dissertation is applied in the context of multi-scale modeling and experimental design. The impact of radiation damage on hardening of irradiated materials is investigated by using the results of SRSCD as inputs into polycrystalline crystal plasticity simulations. In addition, the temperature shift required to achieve equivalent damage accumulation during irradiation at different dose rates, such as in the case of using ion irradiation as a proxy for neutron damage. The scientific developments presented in this dissertation represent significant improvements over the state of the art due to improved simulations of defect accumulation and direct upscaling of results into polycrystalline plasticity models. The tools and understanding of defect behavior developed here will allow predictive modeling of metal degradation in reactor-relevant damage environments, including the defected microstructure and macroscopic material property changes due to irradiation.