arXiv subjects

G. Demange

Publications and source records attributed to G. Demange.

3 recordsLinked to original sources

arXiv2021

Fcc -> bcc phase transition kinetics in an immiscible binary system: atomistic evidence of the twinning mechanism of transformation

Extensive atomistic simulations based on the quasiparticle (QA) approach are performed to determine the momentous aspects of the displacive fcc/bcc phase transformation in a binary system. We demonstrate that the QA is able to predict the major structural characteristics of fcc/bcc phase transformations, including the growth of a bcc nuclei in a fcc matrix, and eventually the formation of an internally twinned structure consisting in two variants with Kurdjumov-Sachs orientation relationship. At atomic level, we determine the defect structure of twinning boundaries and fcc/bcc interfaces, and identify the main mechanism for their propagation. In details, it is shown that twin boundaries are propagated by the propagation of screw dislocations in fcc along the <-1-11>_α direction, while the propagation of fcc screw dislocations along coherent terrace edges is the pivotal vector of the fcc/bcc transformation. The simulation results are compared with our TEM and HRTEM observations of Fe-rich bcc twinned particle embedded in the fcc Cu-rich matrix in the Cu-Fe-Co system.

cond-mat.mtrl-sci↗

arXiv2016

Snowflake growth in three dimensions using phase field modelling

Snowflake growth provides us with a fascinating example of spontaneous pattern formation in nature. Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active scientific fields, ranging from pattern formation in physical and chemical systems, to self-assembly problems in biology. Yet, very few models currently succeed in reproducing the diversity of snowflake forms in three dimensions, and the link between model parameters and thermodynamic quantities is not established. Here, we report a modified phase field model that describes the subtlety of the ice vapour phase transition, through anisotropic water molecules attachment and condensation, surface diffusion, and strong anisotropic surface tension, that guarantee the anisotropy, faceting and dendritic growth of snowflakes. We demonstrate that this model reproduces the growth dynamics of the most challenging morphologies of snowflakes from the Nakaya diagram. We find that the growth dynamics of snow crystals matches the selection theory, consistently with previous experimental observations.

physics.comp-ph↗

arXiv2016

A rational use of BCA code MARLOWE for ballistic effects of ion beam irradiation in the ion mixing formalism: comparison to Molecular Dynamics

Understanding ballistic effects caused by ion beam irradiation, and linking them with induced structure can be a key point for controlling and predicting the microstructure of irradiated materials. For this purpose, we have investigated ballistic effects from an ion mixing formalism point of view. The displacement cascades in copper and AgCu alloy were obtained using binary collision approximation (BCA) and molecular dynamics (MD) simulations. We employed BCA-based code MARLOWE for its ability to simulate high energy displacement cascades. A first set of simulations was performed using both methods on pure copper for energies ranging from 0.5 keV to 20 keV. The results of BCA and MD simulations are compared, evidencing rationally parametrized MARLOWE to be predictive. A second set of simulations was then carried out using BCA only. Following experimental studies, AgCu alloy was subjected to 1 MeV krypton ions. MARLOW simulations are found to be in good agreement with experimental results.

cond-mat.mtrl-sci↗