Ultralow friction behaviour of B4C-BN-MeO composite ceramic coatings deposited on steel

Boron based ceramic coatings were deposited on steel substrates by high-energy short pulse laser melting. Under conditions of the laser deposition, coatings consisted of boron carbide and boron nitride form a layer that acts as solid lubricant leading to a low coefficient of friction (COF). The COF could be drastically decreased by proper selection of chemical composition of boron based ceramic coatings. Ultimately low COF of 0.03 was registered during dry sliding tests of coatings with addition of different metal oxides (MgO, ZrO2, Li2O). Low COF of composite ceramics coatings was attributed to the formation of the BO bond observed by the X-ray photoelectron spectroscopy technique. This bond as the essential component of the internal structure of coatings explains ultralow friction behaviour and remains low even during gradual deterioration of the coating. High quality adhesion of ceramics to steels was explained by reactive phase formation at the steel-ceramic interface, which was confirmed by both transmission electron microscopy and X-ray diffraction. •Ceramic coatings based on B4C, h-BN and metal oxides were deposited on steel.•Metal oxides significantly reduce the coefficient of friction.•Appearance of BO bonds in the coatings explains ultralow friction behaviour.•Addition of Li2O provides the lowest coefficient of friction.•Adhesion of coatings is provided by a reactive wetting at the steel substrate.