Precipitate stability and morphology in irradiation environments

Abstract

A solid under irradiation constitutes a nonequilibrium dynamical system, and therefore the modeling of phase stability in such systems requires a kinetic approach. This paper presents some recent advances in the atomistic modeling of precipitation under irradiation, using kinetic Monte Carlo simulations. It illustrates that vacancy-assisted and thermodynamically driven phase separation, in competition with forced atomic mixing promoted by nuclear collisions, can lead to three very different outcomes: dissolution of pre-existing precipitates, the formation of compositional patterns at the nanoscale, or macroscopic decomposition. Interstitial transport, on the other hand, when coupled with solute fl uxes, can induce the precipitation of mushy precipitates, even in ideal alloy systems. These diverse phase evolutions are shown to be rationalized by continuum modeling.

Atomistic mechanism of cyclic phase transitions in Nd–Fe–B based intermetallics

“…These EXAFS results are in good qualitative agreement with the predictions of Kinetic Monte Carlo (KMC) simulations reported by Soisson [45] and Krasnochtchekov et al [41], who suggest that while atomic mixing can extend solubility limits, create disorder in ordered alloys, and result in amorphization; it cannot bring about solute segregation or precipitation. For precipitation to occur a high concentration of point defects (vacancies and/or interstitials) is required; the irreversible annihilation of these point defects, either by vacancy-interstitial recombination or by vacancy elimination at sinks, leads to redistribution of alloy atoms, resulting in precipitation.…”

“…Instead, based on the theoretical models [39] and computer simulations [40,41] of MM, we assumed milling induced forced random mixing of Nd and Fe atoms in the Nd 2 Fe 14 B intermetallic and modeled this This model was used in the ATOMS 3.0 program to generate input file for the FEFF6.1 code used to determine the theoretical EXAFS function. The first shell EXAFS fitting of mechanically milled samples ( Fig.…”

“…The value of edge energy correction for all samples was less than 4 (AE0.2) eV. The atomic rearrangement during these processes involved redistribution of alloy atoms [41,44,45] resulting in the enrichment of Fe atoms in some regions and the precipitation of a-Fe nanocrystals in the amorphous phase.…”

Radiation-Induced Segregation

“…16 A case of homogeneous RIP, due to a mechanism similar to the one proposed by Cauvin and Martin 52 (see Section 1.18.2.4), has been simulated with a simplified interstitial diffusion model. 130,131 The application of AKMC to real alloys has just been introduced. Copper segregation and precipitation in a-iron has been especially studied, because of its role in the hardening of nuclear reactor pressure vessel steels.…”

Migration of rhenium and osmium interstitials in tungsten

“…As well as nuclear transmutations, direct effects of irradiation of materials are atomic displacements, i.e., vacancies, self-interstitial atoms (SIAs) and their clusters. The emergence of RIP is roughly explained as follows: an SIA is binding a solute atom; a vacancy is binding another solute atom; then SIA-vacancy recombination can cause aggregation of solute atoms [14][15][16]. See Fig.…”