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A role of oxi-nitrocarburizing technique for low-carbon steel was intensively evaluated as a means of reducing the problem of corrosion in gas nitrocarburizing, which is a vital disadvantage of gas nitrocarburizing. Oxi-nitrocarburizing was carried out by a two-step process: Gas nitrocarburizing at 560 °C and oxidation. In order to characterize two different methods of oxi-nitrocarburizing, oxidation was performed under two different conditions: Air and steam as oxygen sources. To analyze the microstructural, physical, and chemical properties of the thin oxide layer and nitride layer, which are the surface hardened layers formed on low-carbon steel by oxi-nitrocarburizing, several methods, such as electron probe microanalysis (EPMA), electron backscattered diffraction (EBSD), scanning electron microscopy (SEM), nanoindentation tests, and potentiodynamic polarization tests were applied. The results indicated that the EPMA and EBSD methods are powerful techniques for the analysis of microstructure, such as phase analysis and metallic element distribution in the oxide layer of magnetite and compound layer of ε-phase and γ'-phase, for oxi-nitrocarburized low-carbon steel. Additionally, the nanohardness using the nanoindentation test and corrosion resistance using the potentiodynamic polarization test for the oxi-nitrocarburized specimens are useful methods to understand the mechanical and corrosion properties of the surface hardened layer.

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Materials with very small dimensions exhibit different physical and mechanical properties compared to their bulk counterparts. This becomes significantly important for the thin films that are widely used as components in micro-electronics and functional materials. In this study, a chromium (Cr) thin film was deposited on a silicon (Si) wafer by DC-magnetron sputtering. The intrinsic hardness of the Cr thin film on Si-wafer was evaluated by the nanoindentation method. We especially investigated ways of measuring the intrinsic hardness of the Cr thin film, and influential factors including the substrate effect and surface roughness effect. To further characterize the intrinsic hardness of the Cr thin film on Si-wafer, we used Xray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Two additional methods, the Meyer-plot and a profile for hardness versus indentation depth, were also employed. As a result of these two methods, we found that the profile for hardness versus indentation depth was valuable for evaluating the intrinsic hardness of Cr thin film on a Si-wafer substrate. The measured intrinsic hardness of the Cr thin film and Si wafer were about 900 Hv and 1143 Hv, respectively. The profile for hardness versus indentation depth can be widely used to evaluate the intrinsic hardness of metallic thin films on substrates.