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 while 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 the mathematical geometric relationship because of the sink-in and pile-up effects confirmed by the finite element analysis (FEA) and optical microscope results. 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.