Hierarchical Upscaling Method for Predicting Strength of Materials under Thermal, Radiation and Mechanical Loading: Irradiation Strengthening Mechanisms in Stainless Steels

摘要

Stainless steels based on iron-chromium-nickel (Fe-Cr-Ni) alloys are the most popular structural materials used in reactors. High energy particle irradiation in these types of polycrystalline structural materials usually produces irradiation hardening and embrittlement. The development of predictive capability for the influence of irradiation on mechanical behavior is important in materials design for next-generation reactors. Irradiation hardening is related to structural information crossing different length scales, such as composition, dislocation, and crystal orientation distribution. To predict effective hardening, the influence factors along different length scales should be considered. A multiscale approach was implemented in this work to predict irradiation hardening of Fe based structural materials. Three length scales are involved in this hierarchical upscaling method: nanometer, micrometer, and millimeter. In the microscale, molecular dynamics (MD) was used to predict the edge dislocation mobility in body centered cubic (bcc) Fe and its Ni and Cr alloys. On the mesoscale, dislocation dynamics (DD) models were used to predict the critical resolved shear stress (CRSS) from the evolution of local dislocation and defects. In the macroscale, a viscoplastic self-consistent (VPSC) model was applied to predict the irradiation hardening in samples with changes in texture. The effects of defect density and texture were investigated. Simulated evolution of yield strength with irradiation agrees well with the experimental data on irradiation strengthening of stainless steel 304L, 316L, and T91. The hierarchical upscaling method developed in this project can provide a guidance tool to evaluate performance of structural materials for next-generation nuclear reactors.