2022
ACLN
|
De Backer, A.; Souidi, A.; Hodille, E.A.; Autissier, E.; Genevois, C.; Haddad, F.; Della Noce, A.; Domain, C.; Becquart, C.S.; Barthe, M.F., 'Multi-Objective Optimization of the Nanocavities Diffusion in Irradiated Metals', Physical sciences forum 5 41 (2022) doi:10.3390/psf2022005041
Materials in fission reactors or fusion tokamaks are exposed to neutron irradiation, which
creates defects in the microstructure. With time, depending on the temperature, defects diffuse and
form, among others, nanocavities, altering the material performance. The goal of this work is to
determine the diffusion properties of the nanocavities in tungsten. We combine (i) a systematic
experimental study in irradiated samples annealed at different temperatures up to 1800 K (the created
nanocavities diffuse, and their coalescence is studied by transmission electron microscopy); (ii) our
object kinetic Monte Carlo model of the microstructure evolution fed by a large collection of atomistic
data; and (iii) a multi-objective optimization method (using model inversion) to obtain the diffusion of
nanocavities, input parameters of our model, from the comparison with the experimental observations.
We simplify the multi-objective function, proposing a projection into the parameter space. Non-
dominated solutions are revealed: two “valleys” of minima corresponding to the nanocavities density
and size objectives, respectively, which delimit the Pareto optimal solution. These “valleys” are found
to be the upper and lower uncertainties on the diffusion beyond the uncertainties on the experimental
and simulated results. The nanocavity diffusion can be split in three domains: the mono vacancy and
small vacancy clusters, for which atomistic models are affordable, the small nanocavities for which
our approach is decisive, and the nanocavities larger than 1.5 nm for which the classical surface
diffusion theory is valid.
|