Through the microscope: Christmas tree or dendrite?

If you visited our website around the turn of the year, you may have spotted the “Christmas tree” on our homepage. Our sample did not come from the forest, however, but from the scanning electron microscope (SEM). The image was simply colourised, creating a rather different materials engineering Christmas greeting.

But what exactly does this image show?

The answer: Dendrites in a shrinkage cavity

The structures are dendrites inside a macroscopic shrinkage cavity in a cast steel housing. Dendrites are tree-like crystal structures that form as a melt solidifies. They develop when the material does not crystallise uniformly during cooling, but instead grows preferentially along particular directions.

In this case, the structure was imaged using a scanning electron microscope and then coloured green, making its dendritic form particularly clear. A typical casting defect was thus transformed into a festive image.

Materials testing with an eye for detail

This example shows that seemingly simple images from materials testing often reflect complex relationships in materials science. Dendritic structures can, for example, provide information about:

• solidification conditions during casting
• local differences in composition
• potential defects such as shrinkage cavities or porosity

Such images are therefore not only visually interesting, but also provide valuable information for analysing cast components.