Scratch test ASTM C1624, DIN V ENV 1071-3
The scratch test is used to determine the bonding strength between a coating and the base material. A diamond stylus is drawn with increasing load across the coating system being tested. Then the resulting scratch mark is evaluated. Various coating defects such as cracks or spalling can be observed in the course of the scratch test. For example, layer separation can be analysed by means of microscopic examination. The critical load under which spalling is first observed is determined as a measurement for layer adhesion. In addition, the frictional force and acoustic emissions are recorded during the measurement and used to support the interpretation of the results.
Scratch test of DLC on steel. Critical load at 35 N. The critical load is determined through optical analysis of crack formation and spalling of the layer, or by analysing the acoustic emissions during scratching. Changes in the friction coefficient during scratching can also be used for evaluation.