Crystal orientation effects on irregular vs. regular growth patterns in faceted/nonfaceted eutectics

The composite growth dynamics, in particular the transformation from irregular to regular patterns, in eutectic alloys that solidify by involving a faceted (f) and a nonfaceted (nf) solids is poorly understood. It is suspected, but not demonstrated, that the process depends on changes in the interfacial kinetics of facets when control parameters (growth rate, composition, …) are varied, and on crystal orientation. Indeed, the interplay between diffusion controlled growth and crystallographic mechanisms (e.g. micro-twinning) remains obscure. For significant progress, f/nf eutectic microstructures of known solidification history must be inspected in terms of morphology and crystallography. We will explore thin (10 µm) Al-Al3Ni and Al-Si films with typical microstructures generated beforehand by in situ directional solidification. Crystallographic mapping of representative areas will be done by non-destructive Laue micro-diffraction measurements through a sapphire substrate.