Toward the correlation of indentation hardness in micro- and nano-scale: understanding of indentation edge behaviors in Fe–Cr alloys

Nanoindentation hardness tests are used to measure indentation hardness at the micro- and nanoscales and further to predict Vickers hardness on larger scales. Hence, the relationship between Vickers and nanoindentation hardness has gained considerable research interest. Here we introduce the concept of Meyer hardness as a mean contact pressure correctly into the two hardness in order to explain their linear correlation. The Vickers hardness is converted to the Vickers Meyer hardness (HVM) as defined by a load divided by the projected contact area; the Nix–Gao model is used to calculate the bulk-equivalent nanoindentation hardness (H0) from depth-dependent nanoindentation hardness. A linear relationship HVM = 0.86 × H0 is observed in the Fe–Cr alloys with a wide range of elastic modulus to hardness ratios and is suggested to be a universal relationship for various metallic materials. A tangent method can distinguish the indentation edge behaviors such as pile-up, sink-in, and the pseudo-pile-up phenomenon. A novel pile-up correction estimates the real contact area in nanoindentation tests, and actual residual contact area is measured to correct the pile-up around Vickers imprints. The corrected HVM and corrected H0 show almost same values after both pile-up corrections.