2019 Physics/Theoretical Colloquium
 
Thursday, August 15th , 2019
3:45 – 4:45 p.m.
Rosen Auditorium (TA-53, Bldg. 001)
 
 
Refreshments at 3:15pm
 
Speaker:   Enrique Martinez Saez

Theoretical Division, T-1, Los Alamos National Laboratory
 
 
“Understanding Radiation-Induced Segregation and Precipitation in Fe-Cr Alloys Using a Multiscale Modeling Framework”
Abstract: 
 
Nonequilibrium chemical redistribution in open systems exposed to external forces, such as particle irradiation, leads to changes in the structural properties of the material, potentially driving the system to failure. Such redistribution is controlled by the complex interplay between the production of point defects, atomic transport rates, and the sink character of the microstructure, possibly leading to radiation-induced segregation and precipitation, which relate to irradiation-assisted stress corrosion cracking and mechanical property changes. We have recently developed an interaction model for the Fe-Cr system that incorporates physically accurate thermodynamic driving forces and kinetic coefficients as compared to experimental results. The atomic interactions are based on ab initio calculations for both the minimum and saddle point configurations for defect migration. Entropic effects are also considered, leading to a model that faithfully reproduces the complex phase diagram and the tracer and interdiffusion coefficients for the Fe-Cr system. We have implemented this energetic model in a kinetic Monte Carlo (KMC) framework to solve for the evolution of the system under irradiation. I will briefly describe the details of the KMC algorithm and the theory behind it. I will then show how this development has proven successful for studying precipitation kinetics. We have employed this model to analyze the afore-mentioned interplay between alloying elements and irradiation-created defects to understand the effect of ideal defect sinks on Cr concentration profiles, with a particular focus on the role of interface density. We observe that the amount of segregation decreases linearly with decreasing interface spacing. Within the framework of the thermodynamics of irreversible processes, a general analytical model is derived and assessed against the KMC simulations to elucidate the structure-property relationship of this system. Interestingly, in the kinetic regime, where elimination of point defects at sinks is dominant over bulk recombination, the solute segregation does not directly depend on the dose rate but only on the density of sinks. This model provides new insight into the design of microstructures that mitigate chemical redistribution and improve radiation tolerance.