A critical appraisal of the extraction of creep parameters from nanoindentation data obtained at room temperature

Nanoindentation is being increasingly used to obtain creep parameters. The technique allows interrogation of small volumes and relatively rapid acquisition of data. However, the reliability of the methods used to extract creep parameters from experimental data is largely unproven. In the present work, commonly employed procedures are applied to a wide range of materials, for which the creep parameters are already known. The correlation observed between known values of the stress exponent, n, and those obtained using the indentation method is generally very poor. Possible reasons for this are considered. One concern is that primary creep, or other unsteady deformation mechanisms, may be strongly influencing the observed behaviour throughout the test. Taking such uncertainties into account, a procedure is proposed for ranking creep propensities exhibited during nanoindentation under specified conditions.