The effect of carbon on the heterogeneous deformation behavior of a martensite was investigated by multiscale strain distribution analysis using the digital image correlation method. Specially, 18％Ni martensitic steels with and without carbon（0.15C steel and C-free steel, respectively）were studied. Low-magnification observation showed that in both steels, a macroscopic strain distribution was caused by the shape of the specimen. However, high-magnification observation revealed that the strain was concentrated in specific blocks in 0.15C steel, suggesting that its heterogeneous deformation behavior depends on the martensitic structure. Thus, addition of carbon in 18％Ni steel was concluded to cause preferential plastic deformation of the blocks owing to an in-lath plane slip system, which tends to promote heterogeneous deformation.

To improve the durability and adhesion of diamond-like carbon (DLC), research has been conducted on adding a graded metallic element to DLC as an intermediate layer. However, to date, no studies have evaluated the compositional characteristics of DLC films of the graded intermediate layer. Accordingly, in this study, we employ Si-doped DLC (Si-DLC) and investigate the effects of different source gas compositions. Si-DLC is deposited on austenitic stainless steel by radio-frequency plasma-enhanced chemical vapor deposition using a mixture of CH₄ and Si(CH₃)₄ (TMS) as a source gas. Samples are subjected to cross-sectional microstructural observation, x-ray photoelectron spectroscopy, raman spectroscopy, glow discharge optical emission spectroscopy, nanoindentation, Rockwell indentation, and friction and wear tests. Results showed that the deposition rate increased with increasing TMS fraction and that sp³ and Si-C bond ratios increased. However, the hardness and wear resistance decreased with increasing TMS fraction. In addition, excellent adhesion was observed under all conditions, regardless of the TMS fraction.

We demonstrated maskless local-nitriding by utilizing the atmospheric-pressure dielectric barrier discharge (DBD) with the operating gas of nitrogen/hydrogen mixture. First, the electric-field calculation proved theoretically that the DBD extension phenomenon under high temperature is caused by the hirizontal extension of the reduced electric field occurring in the discharge gap. Second, an expectation is deduced from the aforementioned theoretical result that the DBD extension phenomenon can be controlled by the value of the voltage applied to the opposite electrode. This expectation eventually leaded to the actual ignition-area control of DBD in the experiment. Third, the utilization of such DBD, the ignition area of which is under control, to nitriding treatment provided the area-control of the nitrided layer formed on the steel surface. As a consequence, the nitrided area was successfully localized from 400 to 0.8 mm² by decreasing the applied voltage without applying any masks and nitriding stop-off paints where the point electrode of 0.7 mm in diameter is used as the opposite electrode.