Tribological performance of boron-based superhard coatings sliding against different materials

Abstract

A superhard boron-based ceramic coating was deposited on a cylindrical surface of a steel disk by high-energy short-pulse laser melting. During severe sliding friction, the coating can act as a solid lubricant with an ultralow coefficient of friction (COF). In combination with different counterface materials, the coating was subjected to sliding wear tests under boundary lubrication conditions. The obtained results show that resistance to severe adhesive wear and associated surface damage (galling) correlate with chemical inertness of tested materials with respect to boron carbide, which is the main component of the superhard coating. Chemically inert materials such as bronzes and babbitt alloys, while sliding against the boron-based coating, exhibit a transition to low friction behaviour at high normal loads and high sliding rates. In this case, the low COF was attributed to the formation of the B–O bonds. The bond appearance was confirmed by the X-ray photoelectron spectroscopy. On the other side, sliding of aluminium alloys against the boron-based superhard coatings leads to galling due to the reaction of B4C with aluminium at the interface and, associating with this, the extent of Al–B junction growth that occurs on further sliding, so this combination of materials is incompatible.