Methodology for measuring contact pressure to cause failure of ceramics and coatings using softer blunt cones

Abstract

This paper presents results of experiments on the ability of ceramic surfaces to withstand the pressures developed beneath circular contacts which are significantly lower than the indentation hardness of those surfaces. First, a simulated fatigue curve for magnesium oxide crystals is discussed, which establishes a limiting mean pressure below which the surface will not fail by fatigue. This pressure is 0·41 GPa for (001) surfaces of magnesium oxide and compares with the indentation hardness of around 6 GPa. It is shown that the conventional mechanism of fatigue of crystalline solids operates, i.e. dislocation multiplication, work hardening, and crack initiation by dislocation interaction on specific crystallographic planes. Second, it is shown that the same experimental approach can be taken to evaluate the integrity of diamond coatings on single crystal (001) silicon substrates. In addition, it is shown that the mean contact pressure to induce failure is reduced under contact fatigue conditions.