Ceramic hardness testing, i.e. resistance to penetration by a body, cannot be performed with all measuring tools and methods due to its special properties such as brittleness or high hardness. Only the usual methods according to Knoop or Vickers remain. WZR ceramic solutions GmbH carries out the hardness determination according to Vickers.

Hardness tester 4 (Zwick; Figure 2) is used for this purpose, which can be flexibly adapted to the respective material with variable superimposed load. A defined ground diamond (equilateral pyramid) is lowered onto the sample at a specified speed. This diamond tip is then pressed into the material at different depths – depending on the hardness of the material and the load on the test device.

Figure 1: Hardness impression on ceramic under microscope. Lengths of diagonals digitally measured and displayed.

In general, the larger the remaining impression, the less hard the material. The resulting impressions (Figure 1) are then measured and evaluated with high precision using microscopic techniques. All this is done according to the standards DIN 843-3 or DIN 6507-1. These standards cover both ceramics and glass. Thus the hardness can be determined as a parameter for the application, e.g. to characterize the closure resistance or the quality of a coating. The unit indicated here is HV (Vickers Hardness Number). The specification of the test load in Newton (N) is common today. However, the obsolete unit Kilopond (kp) can also be found in some cases. This can be converted to N by a factor of 9.80665.

Figure 2: Hardness tester 4 (Zwick).