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To reduce friction coefficient, hardness is increased by using a nanometer-period multilayer structure and shearing strength is decreased by applying of low-shearing-strength tungsten disulfide and molybdenum disulfide layers. In nanoindentation testing, multilayer films showed a higher hardness and a lower modulus of dissipation energy than single-layer films. In nanoscratch and microwear testing using an atomic force microscope (AFM), both the scratching force and wear rate of multilayer films could be decreased. The friction coefficient of the nanoperiod multilayer film was as low as µ=0.04 in the ball-on-disk tribotest in 52 to 58% humidity conditions. The friction endurance life of the nanoperiod multilayer films evaluated from the cycles in which the friction coefficient increases rapidly is nine times longer than those of single-layer films.

To improve the reliability of high-density magnetic systems, a new thin protective layer against wear and corrosion must be applied on magnetic disk media.Various low-energy beams produced from N2i O2, CF4 and CH4 plasma were irradiated onto Co-Cr-Ta magnetic media, and then the effects on hardness, corrosion resistance and magnetic coercive force were studied, and the following results were obtained.(1) To clarify the relationship between hardness and plasma state, plasma spectroscopy analysis was performed. The hardness was affected by ion and radical quantities in the plasma.

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The world's first 25 kW laser welding machines at its 24-inch pipe mill has been installed. The technology for the high-power laser pipe welding process that assures welds with the same properties as those of the base metal while maintaining high productivity has been started to develop. Key technologies for this process such as high power laser welding, high-accuracy seam tracking and nondestructive inspection have been successfully established. The results obtained are as follows.(1) The productivity of this process is much higher than conventional fusion weldings, e.g., SAW for less than steel plate 16 mm thick.(2)High energy density of laser beam helps to produce finely distributed oxides.