No abstract

Zirconium alloys are currently used in nuclear power plants where they are submitted to hydrogen pick-up. Hydrogen in solid solution or hydride precipitation can affect the behavior of zirconium alloys during service but also in long term storage and in accidental conditions. Numerical modeling at mesoscopic scale using a "phase field" approach has been launched to describe hydride precipitation and its consequences on the mechanical properties of zirconium alloys. To obtain realistic results, it should take into account an accurate kinetic, thermodynamic, and structural database in order to properly describe hydride nucleation, growth, and coalescence as well as hydride interaction with external stresses. Therefore, an accurate structural characterization was performed on Zircaloy-4 plates and it allowed us to identify a new zirconium hydride phase called . The phase has a trigonal symmetry and is fully coherent with hcp ␣Zr. The consequences of this new zirconium hydride phase on hydride transformation process and stressreorientation phenomenon are discussed. A first attempt to numerically model the precipitation of this new zirconium hydride phase has been undertaken using the phase field approach.

We present a quantitative phase-field modeling of radiation-induced segregation in Fe-Cr alloys. The evolution of chemical and point defect concentration fields are described by an Onsager formalism combined to a Cahn-Hilliard like diffusion equation for the introduction of non-uniform driving forces. Both the Onsager transport coefficients and the driving force parameters are extracted from atomic Monte Carlo simulations with point defect diffusion models fitted on DFT calculations, in a composition range between 0 and 20 at.% Cr and in a temperature range between 600 and 1000 K. Phase-field simulations are able to quantitatively reproduce the evolution of segregation profiles obtained from direct atomistic kinetic Monte Carlo simulations, while being typically two orders of magnitude faster. It is shown that a precise parameterization of the concentration-dependent Onsager transport coefficients, thermodynamic factors, and equilibrium point defect concentrations is crucial for the phase-field method to be quantitative.