Methods for the determination of the real tip shape of Vickers and Berkovich indenters

摘要

The real tip shape of diamond pyramids as indenter has a strong influence on the hardness and modulus results for indentation depths below 1μm. The preparation process does not allow to reduce the tip curvature to a radius smaller than about 0.2 μm. The measurement error in this depth range is therefore 20% and more. Hence, for accurate measurements an area function is absolutely necessary. The tip rounding can be determined by wholly elastic measurements with very low loads into hard reference materials. For the determination of the complete area function two methods are available: The direct method consists in the measurement of the tip shape with a calibrated AFM. With the indirect method the contact area is calculated from indentation experiments with different loads into carefully selected reference materials. It is shown that the area functions of both methods agree well for the investigated materials if additional corrections are used.