Novel nanoindentation strain rate sweep method for continuously investigating the strain rate sensitivity of materials at the nanoscale

TL;DR

This paper presents a novel nanoindentation technique that allows continuous measurement of strain rate sensitivity across a wide range of strain rates at the nanoscale, improving upon traditional discrete methods.

Contribution

The paper introduces a new nanoindentation method enabling continuous strain rate sensitivity measurement, overcoming limitations of discrete strain rate jump tests.

Findings

Method works across various materials including metals and glasses.

Discrepancies observed are mainly due to nanoindentation size effects.

The technique is robust if size effects are properly corrected.

Abstract

We introduce a new nanoindentation method to continuously measure the hardness while sweeping through orders of magnitudes of strain rates within a single experiment. While nanoindentation already allows the determination of the strain rate sensitivity of materials by means of strain rate jump tests, these are typically limited to few discrete strain rates. With the new method, the strain rate sensitivity can be measured continuously as a function of the strain rate. Applications to fused silica, Zn-22 %Al superplastic alloy, single crystalline aluminum, various nanocrystalline metals and a palladium-based metallic glass are shown. Besides some discrepancy with the reference measurements, the new method seems only affected by the presence of a strong nanoindentation size effect. Provided this indentation size effect is not excessively large and can be corrected for accurately, the method proves robust, with no suggestion that the direction of the strain rate sweep affects the evaluation of the strain rate sensitivity.