Relevance of instrumented micro-indentation for the assessment of hardness and Young's modulus of brittle materials

Using instrumented micro-indentation technique, Vickers hardness and Young's modulus were measured of several brittle materials. Results are compared to values obtained using conventional techniques. It is shown that the reliability of the instrumented indentation technique is mostly affected by the surface finish of the indented surface, the sample fixture and the applied load. Among the possible sources of discrepancy between instrumented indentation and conventional techniques is surface damage occurring in the micro-load range. For the materials studied in this work, it is demonstrated that a maximum applied load of 1000 mN should be used in order to prevent the deleterious effects of micro-cracking and associated artefacts (enhancement of materials compliance due to cracking). The influence of creep is shown to remain negligible for the range of experimental conditions used. When the experimental difficulties of working with very stiff and brittle materials are remedied, instrumented micro-indentation provides Young's modulus and Vickers micro-hardness values close to those obtained using classical techniques (i.e. within 10–15%).