Development of super-tribological duplex coatings due to 3-dimensional femtosecond-laser processing

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(1) Femtosecond-laser-induced nanostructure formed on hard thin films of TiN and DLCTribological hard coatings of TiN and DLC were irradiated by 800- and 267-nm, femtosecond (fs) laser pulses in air at an energy fluence slightly above the ablation threshold. On the ablated thin-film surfaces, the linearly-polarized fs pulses produce arrays of fine periodic structures that are almost oriented to the direction perpendicular to the laser polarization, while the circularly-polarized light forms fine dot structures. The size of these surface structures is 1/10 〜 1/5 of the laser wavelength and decreases with a decrease in the laser wavelength. Furthermore, the size of these structures increased with an increase in the fluence. The results suggest that the surface morphology can be controlled precisely with the fs-laser polarization and wavelength and fluence.(2) Development of DLC-MoS_2 duplex thin films and the influence of micro grooves against the tribological propertyMicro-sized grooves were mechanically created in the center of the sliding path of a ball-on-disk friction testing machine on a DLC coating and then deposited with a solid lubricant film of MoS_2 with a thickness of about 3 μm utilizing a sputtering method. The friction coefficient was lowered from 0.16 to 0.09 due to the micro-grooves against the bearing steel ball. These results suggest that the micro-grooves act as MoS_2 lubricant reservoirs. The fs-laser processing should be applied to create the more fine micro-grooves.(3) The influence of femtosecond-laser-induced nanostructure against the tribological propertyWe developed the technique to create a nanostructured area (10mm X 10mm) on a DLC film utilizing the fs-laser pulses. It was found that the nanostructured DLC surface showed the improved tribological properties against the bearing steel ball.