Résumé:

Most metals and ceramics are aggregates of crystalline grains. Grain-boundaries (GBs) are two-dimensional lattice defects that separate the different grains and that control the bulk mechanical properties of polycrystalline materials. In particular, the sliding and the migration of GBs play important roles in the plastic deformation. Moreover the plastic behaviour depends crucially on the size of the crystallites. Colloidal polycrystals behave as most metals and ceramics at larger time and length scales, allowing to investigate their morphology and mechanical properties by direct 3-D visualization. In this talk I will show how the texture of a colloidal model polycrystalline system is tailored by adding controlled amounts of impurity and by changing the speed of crystallization. The morphology is analyzed quantitatively by confocal microscopy and for the first time the kinetics of growth of the crystallites, the distribution and the role of the impurities during solidification is observed proving theoretical predictions not detectable in molecular systems.