#optical microscopy

Al 75, Cu 25 (wt%), hypoeutectic alloy

Processing: Sand cast

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Sample preparation: Etched in sodium hydroxide solution

Technique: Reflected light microscopy

Length bar: 40 μm

Further information: The micrograph shows primary Al dendrite arms (white). The dendrite trunk has been intersected at an angle by the plane of polishing to give the observed morphology. Between the dendrites is the Al - CuAl₂ eutectic. Initially dendrites would have formed from the liquid, the regions between the dendrite arms known as the mushy zone transforming to a eutectic solid (L to Al + CuAl₂). These two phases form cooperatively as neighbouring lamellae with the lateral diffusion of material across the growing interface. The relative amounts of the two phases (Al and CuAl₂ ) within the eutectic are determined by applying the Lever Rule at the eutectic temperature.

Contributor: Prof T W Clyne

Organisation: Department of Materials Science and Metallurgy, University of Cambridge

Source. 

themicroscopist:

Optical and scanning electron microscope images, as well as elemental maps of a gear in a watch.