Nanoindentation of nanocrystalline Ni with geometrically different indenters

Nanoindentation has been used extensively for characterization of mechanical properties of materials in small scales and thin films. Traditionally, it is assumed that measured values for hardness are independent of indentation size. The indentation size effect (ISE) and the effect of indenters’ geometry have been investigated in this research. Nickel and nickel-based materials have received more interests recently for application of structural components in MEMS industries and also in the basic research. Hardness of electrodeposited nanocrystalline and commercially produced microcrystalline pure nickel were determined by using three geometrically different nanoindneters. The highest hardness values are for the Conical and the lowest for Berkovich indenters at the same indentation depths. The hardness measurements obtained from Berkovich and Cubecorner show good agreements with the mechanism-based strain gradient plasticity model. The results also indicate that the ISE strongly depends on each indenter’s geometry and is less sensitive to indentation depth. There is negligible strain rate dependency of hardness to the deeper depths and a significant increase in the hardness due to the decrease in grain size.