Formation of steady state size distribution of precipitates in alloys under cascade-producing irradiation (original) (raw)
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Evolution of long-range order and composition for radiation-induced precipitate dissolution
Physical Review B, 1996
Disordering and dissolution of L1 2 ordered ␥Ј precipitates under irradiation at temperatures between room temperature and 623 K are investigated by means of transmission electron microscopy and field-ion microscopy with atom probe. The combination of both experimental techniques allows us to follow the disordering process as well as chemical decomposition of the precipitates with atomic resolution. During room-temperature irradiation and for increasing irradiation fluence, the concentration profiles across the precipitates show a broadening of the ␥ /␥ Ј interface. The experimentally obtained depth profiles can be interpreted assuming a dissolution process of the concentration inhomogeneities due to ballistic transport only. A correlation analysis of the experimental data yields a mixing diffusion coefficient of D mix /Kϭ͑0.75 Ϫ0.4 ϩ0.2 ͒ nm 2 dpa Ϫ1. Depending on irradiation temperature, two dissolution regimes are observed. For a displacement rate of 10 Ϫ3 dpa s Ϫ1 , the precipitates first disorder and then dissolve in a disordered state at temperatures below 540 K, while disordering and dissolution occur simultaneously at temperatures between 540 and 623 K. These results demonstrate that disordering of the precipitates is not necessarily required for the dissolution. The results are in accordance with recent theoretical predictions for the dissolution mechanism of ordered precipitates under irradiation. ͓S0163-1829͑96͒07629-1͔
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We investigate the fundamentals of compositional patterning induced by energetic particle irradiation in model A-B substitutional binary alloys using kinetic Monte Carlo simulations. The study focuses on a type of nanostructure that was recently observed in dilute Cu-Fe and Cu-V alloys, where precipitates form within precipitates, a morphology that we term "cherry-pit" structures. The simulations show that the domain of stability of these cherry-pit structures depends on the thermodynamic and kinetic asymmetry between the A and B elements. In particular, both lower solubilities and diffusivities of A in B compared to those of B in A favor the stabilization of these cherry-pit structures for A-rich average compositions. The simulation results are rationalized by extending the analytic model introduced by Frost and Russell for irradiation-induced compositional patterning so as to include the possible formation of pits within precipitates. The simulations indicate also that the pits are dynamical structures that undergo nearly periodic cycles of nucleation, growth, and absorption by the matrix.
Precipitate growth kinetics under inhomogeneous concentration fields using a phase-field model
Physical Review Materials, 2021
We investigate precipitation dynamics in the presence of a local solute gradient using phase-field simulations. During the homogenization heat treatment of the solidified Inconel 718 alloy, high Nb concentration within the Laves phases or at the core of the secondary arms results in Nb diffusion into the γ matrix. The volume fraction and spatial distribution of precipitation during subsequent annealing can be controlled by tailoring the Nb concentration gradient in the matrix during homogenization. We use a surrogate Ni-Fe-Nb alloy for Inconel 718 to explore the growth dynamics of δ precipitates related to the local Nb concentration levels. The simulations indicate that in the presence of a Nb concentration gradient the growth rate of δ precipitates is higher than in a matrix of uniform average Nb concentration. The higher growth rate is a result of the higher local thermodynamic driving force at the interface between the solute-rich matrix and the δ interface. We propose a phenomenological model to describe the diffusion-controlled growth kinetics of the δ phase under a solute concentration gradient.
Journal of Nuclear Materials, 2007
We consider below kinetics of copper precipitate clustering in model FeCu alloys under cascade-damage irradiation. The investigation is carried out for rather high copper content compared with the solubility limit. The nucleation and growth stage preceding the coarsening kinetics is analysed. It is assumed that atomic collision cascades create embryos that are the growing centers during supersaturation decay. The time dependencies of copper precipitates characteristics are obtained as a solution of the Fokker-Planck equation for clusters in the space of their sizes. The results are in a qualitative agreement with some experimental data on copper clustering under neutron irradiation.
Non-classical nuclei and growth kinetics of Cr precipitates in FeCr alloys during ageing
Modelling and Simulation in Materials Science and Engineering, 2014
In this manuscript, we have quantitatively calculated the thermodynamic properties of the critical nuclei of Cr precipitates in FeCr alloys. The concentration profiles of the critical nuclei and nucleation energy barriers were predicted by the constrained shrinking dimer dynamics method. It is found that Cr concentration distribution in the critical nuclei strongly depends on the overall Cr concentration as well as on the temperature. The critical nuclei are non-classical because the concentration in the nuclei is smaller than the thermodynamic equilibrium value. These results are in agreement with atomic probe observation. The growth kinetics of both classical and non-classical nuclei was investigated by the phase-field approach. The simulations of critical nucleus evolution showed a number of interesting phenomena: (1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; (2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics and (3) a critical classical nucleus grows faster at the earlier growth stage than does a non-classical nucleus. All of these results demonstrate that it is critical to introduce the correct critical nuclei in order to correctly capture the kinetics of precipitation.