Breviary Technical Ceramics






5.3.5 Hardness

Hardness implies a high resistance to deformation and is associated with a large modulus of elasticity. Technical ceramic components are therefore characterised by their stiffness and dimensional stability.
The high hardness of technical ceramics results in favourable wear resistance. Ceramics are thus good for tribological applications. Material type and microstructure strongly influence the wear resistance.

Figure 89: A guide to the flexural strength and hardness of selected materials

The high hardness of ceramic materials is at the expense of a lack of plastic deformation (ductility) that could absorb stress concentrations. The part could break without warning (see figure 80).

Test procedures for determining the hardness according to Vickers, Knoop and Rockwell are specified in DIN EN 843-4. It is usual to quote the Vickers hardness HV [MPa], although it is important to quote the test force (in kg) as the result is very dependent on that. The values of HV0,1 and HV50, for instance, may differ by about 30 %.
In practice, it has been found that quoting HV10 values is useful for ceramics.

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