Do residual nano indentations in metals and ceramics relax with time?

An atomic force microscopy study of relatively large residual Berkovich, Vickers and spherical nano indentations in four metals and two ceramics (high-temperature superconductor YBCO and polycrystalline silicon nitride) is described. It is shown that residual nano indentations in these materials, which are free from extensive cracking, change of temperature and environmental attack, do not show any measurable relaxation even over a period of up to two years. This fact, combined with our previous continuous in situ observations from indentation experiments on MgO single crystals, indicates that careful and detailed investigations of nano indentations with metrological atomic force microscopes can be carried out, without there being a risk of any measurable relaxation, either in their dimensions or profiles, even well after the indentations have been made.