Metallography with Color and Contrast

The examination of the sample in polarized light is also often helpful in cases where color etching fails to provide the desired contrast of individual microstructure components, or if only one phase is attacked in composite materials. Examples are shown in Figures 19 to 21. Figure 19 shows a much better image of the grain and twin structure in a 10 cent coin made of Nordic gold, while in Figure 20, individual crystals and their needle structure can be seen in tungsten carbide. Figure 21 shows the amount, size and shape of graphite fibers in black, carbon fiber reinforced plastic. If documentation is required of the different components of a composite material, additional optical contrasting is usually essential. Figure 22 documents the excellent result that can be achieved by optical imaging of the microstructure of special brass and, at the same time, the glass fiber braid coating. In the photo of a severed capacitor, the glass fiber core can be seen in its thin copper sleeve welded onto a conductor track of tin bronze (Figure 23). The last photo of this series shows an anti-wear sintered layer of tin bronze with graphite components and ceramic particles (Figure 24).

These examples clearly demonstrate that the distribution and formation of different phases are of great, if not overriding, significance for the properties of the material. This is why clear differentiation with the method presented here is particularly important.

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