Formation dynamics of solidification microstructures of metallic alloys: characterisation by synchrotron X-ray imaging

We studied in situ and real-time the directional solidification of thin samples of binary alloys and a quasicrystal using both X-ray radiography and topography techniques. On Al-3.5 wt%Ni non-refined alloys, we studied the formation of the initial state and the solidification front morphology (cellular then dendritic growth). Mechanical strains were highlighted. The Columnar to Equiaxed Transition was studied on Al-3.5 wt%Ni refined alloys. We described the blocking of the columnar front and the following equiaxed growth regime. The refining particles efficiency reaches a limit. An analysis of the microstructure morphology was performed. The study of the i-AlPdMn quasicrystal shows the growth of faceted dodecahedral grains. Thermo-solutal convection effects were highlighted. Strain visualisation shows a strong deformation of grains. The apparition of porosity was observed during fusion of grains. (author)