Plasma nitriding of stainless steels has been investigated over a range of temperature from 400 to $500^{\circ}C$ and time from 10 to 20 hours. Characterization of systematic materials was carried out in terms of mechanical properties and corrosion behaviors. The results showed that plasma nitriding conducted at low temperatures not only increased the surface hardness, but also improved the corrosion resistance of STS 316L, STS409L, and STS 420J2. It was found that plasma-nitriding treatment at $500^{\circ}C$ resulted in increasing the corrosion performance of STS 409L and STS 420J2, while STS 316L was observed with server and massive damage on surface due to the formation of CrN.

Recently, renewable energy sources such as wind turbine, solar cell are interested in preventing global warming which is caused by the consumption of fossil fuel. SCM440(H) and SNCM439 have been used in the major components of the wind turbine gear because of excellent mechanical properties. In the present study, the heat treated mechanical properties of SCM440(H) and SNCM439 with 150 mm diameter were compared with those with 25 mm diameter which is generally accepted material for structural application. Heat treated SCM440(H) showed better mechanical properties such as tensile strength, hardness and impact absorbed energy compared with those in SNCM439. Hardenss value between as-quenched and as-quenched followed by tempering showed big difference in SNCM439, however the difference in SCM440(H) was relatively small. Heat treated mechanical properties of the alloys with 25 mm diameter were more uniform value than those with 150 mm diameter.

Al-Co/AlN-Co multilayer films with different layer thicknesses were prepared by using a two-facing target type D.C sputtering (TFTS) system. The deposited films were annealed isothermally at different temperatures and their microstructure, magnetic properties and resistivity were investigated. The magnetization of as-deposited films is very small irrespective of layer thickness. It was found that annealing conditions and layer thickness ratio (LTR) of Al-Co to AlN-Co can control the microstructure as well as the physical properties of the prepared films. The resistivity and magnetization increase and the coercivity decreases with decreasing LTR. High resistivity and sufficient magnetization were obtained for the films with LTR = 0.35. Films having such considerable magnetization and resistivity will be a potential candidate to be used for a high density recording material.

This study was carried out to investigate the effect of aging treatment on the mechanical properties and damping capacity of 12Cr heat resistant steel with ferrite phase. While hardness values in ferrite phase was not changed, that in martensite phase was dramatically dropped in early stage of aging treatment and then gradually decreased with increase of aging time. As aging treatment was carried out, the precipitation was not detected in ferrite phase, while carbides were precipitated in martensite phase. With increasing the aging time, tensile strength eventually decreased while impact toughness increased rapidly in the early stage of aging and then gradually increased. Besides, it was confirmed that damping capacity was not changed in the early stage of aging and then gradually increased with increase of aging time.

$TiO_2$ films were deposited on a glass substrate with RF magnetron sputtering and then surface of $TiO_2$ films were electron beam irradiated in a vacuum condition to investigate the effect of electron bombardment on the thin film crystallization, surface roughness and gas sensitivity for hydrogen. $TiO_2$ films that electron beam irradiated at 450eV were amorphous phase, while the films irradiated at 900 eV show the anatase (101) diffraction peak in XRD pattern. AFM measurements show that the roughness is depend on the electron irradiation energy. As increase the hydrogen gas concentration and operation temperature, the gas sensitivity of $TiO_2$ and $TiO_2$/ZnO films is increased proportionally and $TiO_2$ films that electron beam irradiated at 900 eV show the higher sensitivity than the films were irradiated at 450eV. From the XRD pattern and AFM observation, it is supposed that the crystallization and rough surface promote the hydrogen gas sensitivity of $TiO_2$ films.

High temperature wear of AlCrN coated tool steels sliding against the ultra-high strength boron steels used for hot press forming has been studied. The sliding wear tests have been carried out using a pin-on-disc of configuration under applied normal load of 50 N for 20 min with heating the ultra-high strength boron steels up to $800^{\circ}C$. Characterizations of tribolayers formed on the contacting surfaces between the tribopairs of the AlCrN coated tool steels and the ultra-high strength boron steels have been studied. It was found on the tribolayers of the AlCrN coated tool steels that microcracking and oxides containing Fe and Cr to increase friction coefficient were formed at the early stage of sliding wear, followed by the generation of the smeared oxide layers containing Fe transferred from the tribopair to decrease friction coefficient. This may mainly contribute to very low specific wear rate of the AlCrN coated tool steels sliding against the ultra-high strength boron steels, resulting from oxideoxide contact between the tribopair.