Materialographic lapping

Like grinding with bonded grains, lapping is intended to eliminate surface irregularities and damages in the ceramic sample. It can be used for the preparation steps 

A glass plate provided with a uniform layer of silicon carbide grains is well suited to the lapping of titanium boride and zirconium boride. These samples can then be polished effectively in 20 min or less with diamond paste or a diamond suspension. 

After grinding or materialographic lapping, the preparation process for ceramic materials continues with mechanical polishing. ElectropoUshing is only possible with electrically conductive ceramics, and ion polishing is uneconomical because of its low removal rates. 

The lapping grains remove the material surface, breeldng down in the process and thus adapting as the suteoa bacames progressively finer. 

The viscosity of the lubricant film determines the film thickness and thus the aggressiveness of the grains. 

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Composite disk are used for materialographic lapping. This operation represents a combination of grinding and lapping. The variety of component materials in the composite disk yields the following possible modes of material removal ... 

Figure 16. Schematic representation of grinding, lapping, materialographic lapping, and polishing (from B. Bousfield).

The preparation process for ceramics can be modified by the introduction of materialographic lapping steps. Polishing times must be kept short in order to avoid the formation of relief. Diamond polishing produces a lower relief than polishing with substances of lesser hardness. 

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