Experimental studies of the evolution of cast microstructures and defects

While great advances have been made in predicting the micro-structural evolution during casting through computational simulation, the ability to experimentally verifying the simulations has lagged behind in the case of metallurgical casting. This is largely due to the following experimental difficulties: i) studying high-temperature phenomena in situ, and ii) characterizing the complex three-dimensional structures and their interactions. This is particularly true at the scale of the dendrites, i.e. with a resolution in the order of microns. This paper highlights some of the recent advances in techniques for the evaluation microstructures during both their evolution and their final three-dimensional morphology. This includes the in situ observation methods of confocal scanning laser microscopy, in situ microfocal X-ray radiography of studies, and microfocal tomography. Examples are giving on both the solidification structure and defects, including: hydrogen porosity evolution, grain refinement and Sr-modification, and particle pushing/engulfment/entrapment.