The animation below shows how the temperature gradient in the liquid affects the morphology of the growth front in a pure metal:
The animation referred to the driving force for solidification, which is greater for larger undercoolings. To see why, click here.
When a dendritic structure forms, the dendrite arms grow parallel to the favourable growth directions, normally 〈 100 〉 in cubic metals. Grains which are orientated with the 〈 100 〉 direction close to the direction of heat flow will grow fastest and stifle the growth of other grains, leading to a columnar microstructure. To see more about how a microstructure develops in a casting, see the microstructure of a cast ingot section of the TLP on Casting.
|This micrograph (left) is an image of the 3D structure of dendrites in a cobalt-samarium-copper alloy, taken with a scanning electron microscope .|
|This micrograph (right), taken with a reflected light microscope, shows the appearance of dendrites of a copper-tin alloy when observed as a 2D section through the 3D structure.|