Role of transfer layer on tribological properties of nanocrystalline diamond nanowire film sliding against alumina allotropes

• Tribological properties of nanocrystalline diamond nanowire film
• Super low value of friction coefficient ~ 0.003 of diamond nanowire against Al2O3 ball
• High friction coefficient and high wear loss of diamond nanowire against sapphire and ruby balls

The tribological properties of nanocrystalline diamond nanowire (DNW) film treated in CH4 atmosphere at 400 °C were studied in ambient atmosphere at room temperature using various allotropes of alumina ball as sliding counterbodies. Super low value of friction coefficient (~ 0.003) and extremely high wear resistance (~ 2.8 × 10− 21 mm3/Nm) were observed when the Al2O3 ball slides against the film. In contrast, high friction coefficients with the values ~ 0.06 and ~ 0.07 were observed while using sapphire and ruby balls, respectively. Wear loss was also high ~ 4 × 10− 19 mm3/Nm and 2.8 × 10− 15 mm3/Nm in DNW/sapphire and DNW/ruby sliding pairs, respectively. Such a behavior is fundamentally explained in terms of the chemical nature of the sliding interfaces and surface energy of ball counterbodies. As a consequence, the chemical affinity of Al2O3 ball towards the carbon atoms is less, which resulted in the absence of carbonaceous transfer layer formation on the Al2O3 ball scar. However, in the case of sapphire and ruby balls, the wear track was found to be highly deformed and significant development of carbonaceous transfer layer was observed on respective ball scars. This phenomenon involving transfer layer formation is related to high surface energy and strong chemical affinities of sapphire and ruby balls towards carbon atoms. In such a condition, sliding occurs between film and the carbonaceous transfer layer formed on the ball exhibiting high energy due to covalent carbon bonds that chemically interact and enhance sliding resistance.

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