Conversion between Vickers hardness and nanohardness by correcting projected area with sink-in and pile-up effects

The Vickers hardness test has been widely used for neutron-irradiated materials and nanoindentation for ion-irradiated materials. Comparing the Vickers hardness and nanohardness of the same materials quantitatively and establishing a correlation between them is meaningful. In this study, five representative materials—pure titanium (Ti), nickel (Ni), tungsten (W), 304 coarse-grained stainless steel (CG-SS) and 304 nanocrystalline austenitic stainless steel (NG-SS)—are investigated for comparison. The results show that the relationship between Vickers hardness and nanohardness does not conform to a mathematical geometric relationship because of sink-in and pile-up effects confirmed by finite element analysis (FEA) and the results of optical microscopy. Finally, one new method was developed by excluding the effects of sink-in and pile-up in materials. With this improved correction in the projected area of the Vickers hardness and nanohardness, the two kinds of hardness become identical.