Abstract
Conventional rate theory often uses the mean field concept to describe the effect of inhomogeneous microstructures on the evolution of radiation induced defect and solute/fission product segregation. However, the spatial and temporal evolution of defects and solutes determines the formation and spatial distribution of radiation-induced second phase such as precipitates and gas bubbles/voids, especially in materials with complicated microstructures and subject to high dose radiation. In this work, a microstructure-dependent model of radiation-induced segregation (RIS) has been developed to investigate the effect of inhomogeneous thermodynamic and kinetics properties of defects on diffusion and accumulations of solute A in AB binary alloys. Four independent concentrations: atom A, interstitial A, interstitial B, and vacancy on [A, B] sublattice are used as field variables to describe temporal and spatial distribution and evolution of defects and solute A. The independent concentrations of interstitial A and interstitial B allow to describe their different generation rates, thermodynamic and kinetic properties, and release the assumptions of interstitial generation and sink strength used in the conventional rate theory. Microstructure and concentration dependent chemical potentials of defects are used to calculate the driving forces of defect diffusions. With the model, the effects of defect chemical potentials and mobilities on the RIS in polycrystalline AB model alloys have been simulated. The results demonstrated the model capability in predicting defect evolution in materials with inhomogeneous thermodynamic and kinetic properties of defects. The model can be extended to materials with complicated microstructures such as a wide range of grain size distribution, coating structure and multiphases as well as radiation-induced precipitation subject to severe radiation damage.
Highlights
Low angle grain boundaries (LAGB) exhibited a suppressed radiation-induced segregation (RIS) response when compared to relatively high angle grain boundaries (HAGB), and at the special Sigma coincident site lattice (CSL) boundaries, the RIS of Cr was suppressed (Hu et al, 2012; Field et al, 2013)
In this work the conventional rate theory of RIS has been extended by taking into account inhomogeneous thermodynamic and kinetics properties of defects
In conventional rate theory the total concentration of solute and solvent interstitials is treated as an independent variable and the fraction of the solute interstitial in the total interstitial concentration is assumed to be the same as the solute concentration in the alloy
Summary
Radiation-induced segregation (RIS) and precipitation are important material property degradation mechanisms in irradiated materials (Lam et al, 1978; Odette and Lucas, 1986; Farrell et al, 1994; Akamatsu et al, 1995; Lu et al, 2008; Was et al, 2011; Hu et al, 2012; Nastar and Soisson, 2012; Field et al, 2013; Wharry and Was, 2013; Yang et al, 2016). We extended the rate theory to considers the effect of the inhomogeneous thermodynamic and kinetic properties of defects on RIS in polycrystalline structures. In the conventional rate theory (Was, 2016), three independent variables, i.e., concentrations of atom A, interstitial (A and B) and vacancy (A and B) are used to describe spatial and temporal distributions of solute A and defects. Conventional rate theory assumes that defects on grain boundaries remain their thermal equilibrium concentrations. It should be a reasonable assumption after the system reaches a steady state. The assumption that defects on grain boundaries remain their thermal equilibrium concentrations in the conventional rate theory is released.
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