Reducing indentation size effect in metals by load function selection

Nanoindentation is an integral technique in determining material properties at small length scales. The indentation size effect (ISE) manifests as increasing hardness as indent depths become shallower. This makes material comparison across length scales challenging. The objective of this work is to study how load function parameters influence hardness, especially at shallow depths where the ISE is most critical. Hardness values from indentation loading methods with different hold and cycling sequences were compared from tests on four pure metal samples. Results show a significant decrease in hardness after both long hold and repeated loading profiles. The decrease was larger at shallow depths, and materials with a lower hardness were found to have a larger percent decrease than harder materials. We discuss these observations in the context of Cottrell’s exhaustion creep and recommend that indentation load functions with hold periods or repeated loading be used to minimize observed ISE. Graphical abstract