Growth Structures, Interface Dynamics and Stresses in Metallic Alloy Solidification: In situ Synchrotron X-ray Characterisation

In solidification processing, the physical properties are primarily controlled by the microstructure built in the solid, Thus, materials engineering requires detailed understanding of microstructure formation dynamics. Using in situ and real-time synchrotron X-ray imaging at the European Synchrotron Radiation Facility, the solidification progress in thin metallic alloys is characterized. On Al - 3.5 wt% Ni alloys, disorienting induced by stress accumulation with the development of columnar dendrites is observed. In particular, X - ray radiography shows bending of secondary dendrite arms which, in the columnar to equiaxed transition, can be furthermore precipitated by equiaxed crystal sedimentation. Ledge growth and facetted solid-melt interface are found on AlPdMn quasicrystals. Increasing the solidification rate, the kinetic undercooling becomes sufficient for nucleation and growth of new grains ahead of the columnar grains.