Solidification is possibly the most important step in the fabrication of any metal part. The micrometer-scale structure that forms during solidification sets the physical and chemical structure that will determine the part's ultimate performance. Understanding the microstructural evolution that occurs during solidification is a critical step on the way to being able to predict and control cast parts. However, it is a very difficult problem to solve because solidification occurs inside an opaque material and requires three-dimensional data collection that occurs at size and time scales that have not been experimentally accessible until now.
In this work, we have developed a new data collection method for X-ray computed tomography that has enabled the first high-resolution, 3-D measurements of solidification in a metal. These measurements are used to observe the formation and evolution of solidification patterns and to develop universal relationships to describe these patterns.