Direct calibration of indenter tip geometry by optical surface topography measuring instruments

Instrumented indentation test (IIT) is a depth-sensing hardness test allowing nano- to macro-mechanical characterisation of surface mechanical properties. Indenter tip geometry calibration allows nano-scale characterisation, overcoming the limits of conventional hardness tests. Calibration is critical to ensure IIT traceability and applicability for quality verification in manufacturing processes. The accuracy and precision of IIT are mainly affected by the indenter tip geometry calibration. State-of-the-art indenter tip geometry calibration reports either direct calibration by AFM, which is highly expensive and unpractical for industry, or indirect calibration methods, which are less accurate, precise and robust. This work proposes a practical, direct calibration method for IIT indenter tip geometry by optical surface topography measuring instruments. The methodology is complemented by uncertainty evaluation. The proposed approach is applied to Berkovich and Vickers indenters and its advantages are proven in terms of accuracy and precision of mechanical characterisation on metallic and ceramic material.