Fraunhofer Institute for Surface Engineering and Thin Films IST
Ball-cratering device with three balls.
Abrasive wear-testing of surfaces
The crater grinding wear test (DIN EN 1071-6, EN ISO 26423)
The crater grinding method can be used to precisely determine the wear resistance of coatings and surfaces. A steel ball wetted with an abrasive fluid and rotating against the specimen grinds a crater into the layer to be tested. The wear coefficient can be calculated from the volume of the crater.
Application in quality assurance
The method is suitable for testing coatings with thicknesses ≥ 1 μm. Abrasive wear is very sensitive to changes in coating composition and structure. It can therefore be used as a parameter for evaluating coating quality in production and for optimization during the development of coating systems.
If the crater is ground through the layers into the substrate, the thickness of the layers can be determined from the diameters of the rings. The accuracy of the coating thickness measurement is approx. 0.1 µm, depending on the surface.
Crater wear (abrasive)
Results of the crater grinding process. Wear coefficients of steel and hard coatings.
Calotte crater
3D representation of a crater in a DLC layer made using a profilometer.
Calotte crater imaged with profilometer.
Crater grinding for determining layer thickness
If the crater is ground through the layers into the substrate, the thickness of the layers can be determined from the diameters of the rings. The layer thickness t is then given by the formula: t = (D2-d2)/8R, where D, d = outer and inner ring diameters and R is the sphere radius. The accuracy of the coating thickness measurement is approx. 0.1 µm, depending on the surface. µm.