Abstract : The thesis adresses the implications of anisotropy induced by rough interface growth in directional solidification. They notably include variable growth directions and dramatic morphological effects such as asymmetry, set of very large sidebranches and instabilities. The study is first focused on homogeneous structures before being widened to inhomogeneous situation.
As the growth velocity increases, the growth direction of dendrites turns from a macroscopic direction given by the thermal gradient to a microscopic direction prescribed by the crystalline symmetries. Their exhaustive experimental study has provided here a large number of data whose analysis reveals an internal symmetry. This symmetry leads to the selection of an orientation's law that is function of the Péclet number and of the angular distance between the fixed directions (thermal gradient and anisotropy). However, a new definition of the characteristic size of the growth structures has led the relative orientation of dendrites to only depend on the Péclet number and to be made independent of the angle between the two prescribed directions. This new law is universal since it is no longer parameterized by the intensity of the thermal gradient, the anisotropy features and the nature of the solidified alloy. Finally, the results obtained on homogeneous fronts are locally applied to inhomogeneous fronts. This enables the understanding of the dynamics implied by the variations of structure size, thermal gradient orientation and thermal gradient intensity.