Example: Crack between plasma spray coating and the substrate, Mag. 500x.

Cracks are fractures in brittle materials and materials with different phases. The energy used to machine the sample is greater than can be absorbed. The surplus energy results in the cracks. Cracks do occur in brittle materials and samples with layers. Care has to be taken through- out the complete preparation process. When cutting coated samples, the wheel should pass through the layer(s) first, so that the base material can act as support. Clamping of the sample should be carried out in a way that no damage can occur. If necessary soft packing between sample and clamp has to be used. Mounting: for fragile materials, hot compression mounting should be avoid and cold mountig, preferably vacuum impregnation, should be used instead. Note: vacuum impregnation will only fill cracks and cavities connected with the surface.

Reference: Metalog Guide, page 80-81, Struers A/S, 2610 Rodovre, Dennmark. Note: Image and text by courtesy of Struers A/S company.

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