Comparison of nanoindentation with conventional hardness

Thin films and hard coatings are used as protective and functional coatings in many industrial fields. Key factors in their development and production are mechanical properties because they reflect their quality and performance. In this application report we show how to measure correctly hardness and elastic modulus of thin coatings using nanoindentation.

Characterization of hardness of materials has been done for more than hundred years. First, Brinell and Rockwell hardness measurement using loads in kilograms and tens of kilograms was developed. Later, when more precise measurement of hardness after quenching was required, Knoop and Vickers microhardness measurement methods were developed, using loads down to tens of grams. ISO and ASTM standards exist for all these methods. They are all based mostly on optical evaluation of the imprint and hardness is calculated via optical measurement of the remaining imprint.
This method, however, has several drawbacks: it relies of optical microscope and its ability to measure reliably the imprint dimensions, which is limited. Indentations with length of diagonals of less than a few micrometers are difficult to measure: according to the ISO 6507 standard, the diagonal of the residual impression should at least be 20 μm in order to have sufficient accuracy. The Vickers microhardness method (HVM) also provides only hardness value, which more easily influenced by residual stresses than elastic modulus.

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