in 1988, the LEM is a mixed research unit, which depends on both
CNRS (Centre National de la Recherche Scientifique) and ONERA
(Office National d'Etudes et de Recherches Aérospatiales).
It accommodates scientists from CNRS, ONERA and Universities.
The research activities focus on the understanding of the microstructures
developed in materials, on their formation and evolution with
time, as well as their impact on physical properties, notably
Beyond its many interactions with academic laboratories at international
level, the laboratory is more specifically involved in fundamental
research. Several investigated topics are related to the activities
of the ONERA departments in charge of the understanding and optimisation
of materials for aeronautics and aerospace.
The main goal is to maintain and develop a sound theoretical expertise
on modelling in the field of materials physics, combined with
an experimental expertise in transmission electron microscopy
(TEM) imaging and spectroscopies, and in mechanical testing.
general approach consists in combining experiment, simulation
and theory to study microstructures in relatively complex materials,
especially multicomponent metallic alloys. Multiscale analyses
are privileged, in order to understand the relationship between
atomic structures and bulk physical properties.
At the atomic level, the experimental TEM observations and the
simulations are used to model nanoscopic systems. At that scale,
the predominant phenomena that arise at finite temperatures are
mostly due to chemical atomic interactions with characteristic
length scales of a few nanometers. At larger scales, up to the
micrometer, elastic effects become important and govern the morphologies
that develop in amaterial. The latter can be viewed as a more
or less homogeneous quasi-continuum, which can be dealt with using
phase field theories. At higher scales, the objective is to investigate
and model the behaviour of the microstructures under external
mechanical and thermal fields. This leads to a global description
of the materials according to three scales (micro or atomic, meso
or microstructural, macro or bulk material), thus involving the
typical problems related to multiscale modelling, viz. the development
and combination of models elaborated at different scales.
Atomic scale studies
crystallographic structure, defects and microstructure at equilibrium
and under external fields.
Nanomaterials: structural studies of nanotubes, atomic characterization
of carbon and BN nanotubes, analyses of growth processes.
Quasicrystals and complex intermetallics: Quasicrystallography
and atomic structures of icosahedral quasicrystals, characterization
and modes of motion of dislocations, plasticity of complex intermetallics.
Characterization studies of crystal defects by electron spectroscopy:
dislocations, stacking faults, grain boundaries and precipitates;
calculation of the influence of defects on electronic spectra.
Dynamics of phase transformations: chemical and elastic effects;
formation and evolution of the microstructure in model alloys.
Dislocation dynamics in metals and alloys; dislocation motion
and interactions, formation of structured dislocation networks
at the mesoscopic scale.
Mesoscopic scale and multiscale analyses
of mixtures of different phases, domain and grain growth. Influence
of temperature, influence of partial atomic order and elastic
fields on growth, formation and spatial organization of precipitates.
Dislocation mesostructures: collective dislocation phenomena;
materials with dislocation mobility governed by the atomic structure
of the dislocation core; materials with dislocation mobility
governed by dislocation-dislocation interactions and self-organization
properties of the dislocation populations.
Connection between the physical discrete approach of plasticity
(dislocations) and the continuum mechanical approaches.