Thomas Schuler and Maylise Nastar

L. Messina, L. Huang, P. Camilos, L. Redgrab-Belkacemi, E. Meslin , M. Loyer-Prost

CEA, Université Paris-Saclay, France

KineCluE : a kinetic cluster expansion formalism to compute transport coefficients from atomic scale data

We introduce the kinetic cluster expansion formalism in which transport coefficients are computed as a weighted sum of intrinsic cluster transport coefficients. These cluster transport coefficients are computed using the open-source code KineCluE developped at CEA over the past few years. We will briefly explain the formalism and the capabilities of the KineCluE code, as well as its relation with commonly used materials modelling methods. Then, we will show a series of example of transport coefficients calculations in complex systems, the complexity arising either from the crystallographic structure, the jump mechanisms or the interactions between alloying components. We will end the presentation with preliminary results on concentrated alloys.

The following talk by M. Nastar will demonstrate how results from KineCluE can be used in higher scale models to better understand and predict materials behavior in out-of-equilibrium conditions:

A thermodynamic formulation of semi-coherent precipitation

By relying on an atomic scale characterization of the ferrite-to-austenite phase transformation in Fe-Ni under irradiation, we introduce a thermodynamic formulation of semi-coherent precipitation. Whenever the precipitate eigenstrain is not compensated by an elastic strain, precipitates feature a loss of coherency at the interface, i.e. the number of lattice sites across the interface is not conserved. It occurs through sequences of kinetic mechanisms involving lattice point and dislocation defects, such as the absorption of point defects condensing in precipitates and forming dislocations. In systems submitted to thermal quenching, severe mechanical solicitation or irradiation, point defects are in excess. The removal of these point defects resulting from a semi-coherent precipitation, stabilizes the system, therefore increases the precipitation driving force. We present a simple thermodynamic formulation of the accommodation mechanisms involving point defects. Through the new concept of semi-coherent phase diagram, we rationalize the selection of non-equilibrium phases in the Fe-Ni system under irradiation. We then show how to use KineCluE to compute the concentration of point defects, the metastable solubility limit and the growth rate of semi-coherent precipitates.

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