Tribological behavior of TiN,AlTiN,and AlTiCrN coatings in atmospheric and vacuum environments

In this study,the tribological characteristics of TiN,AlTiN,and AlTiCrN coatings sliding against a SUS420J1 stainless steel pin were investigated in atmospheric and vacuum environments.The coatings were deposited on SUS440C substrates using the arc-physical vapor deposition technique.The friction and wear behavior of the coatings were evaluated based on the systematic analyses of the friction coefficient data as well as the physical and chemical state of the wear track.The results revealed that the friction coefficients of the SUS440C specimen and AlTiCrN coatings increased,whereas those of the TiN and AlTiN coatings decreased when the environment was changed from atmospheric to vacuum.It was confirmed that the formation of an oxide layer and adsorption of oxides on the surface were dominant factors that influenced the tribological behavior in the atmospheric environment.On the other hand,the compatibility,oxidation inhibition,and droplets of the surface mainly affected the frictional characteristics in the vacuum environment.The results of this work are expected to aid in the selection of proper coating materials for tribological systems operating in a vacuum.

Development of polyimide films reinforced with boron nitride and boron nitride nanosheets for transparent flexible device applications

The benefits of reinforcing polyimide （PI） films with boron nitride （BN） particles and boron nitride nanosheets （BNNSs） were assessed with the aim of enhancing their thermal, optical, and mechanical properties for flexible device applications. BNNSs were prepared from BN particles using a liquid-phase exfoliation method assisted by an ultrasonic probe-type sonicator and centrifugator. PI-based composite films blended with BNNSs and BN particles were fabricated at various concentrations via mechanical stirring and spin coating. The transparency of the PI/BNNS composite films remained almost the same as that of pure PI films up to 3 wt.% whereas the transparency of the PI/BN composite films decreased with increasing concentration of the BN fillers at 550 nm. The thermal stability improved significantly with increasing concentrations of both BN and BNNS relative to that of pure PI films. The temperature for 5% weight loss of the PI/BNNS composite film was higher than that of the PI/BN composite film at the same filler concentration. The composite films with 2 wt.% BN or BNNS showed the lowest wear rate, and the PI/BNNS composite films showed more stable frictional behavior compared to the PI/BN composite films. In addition, bending tests showed that the PI/BNNS composite films exhibited excellent flexibility compared to the PI/BN composite films. Overall, the results indicate that the BNNS can be effectively used as a filler that can enhance the thermal and mechanical properties of polymer materials for flexible device applications.