Structural Regulation And Tribological Performances Of Boron Nitride Enhanced Epoxy Composite Coatings

With the exploration of marine resources,marine tribology has gradually attracted our attention.The tribological environment in ocean is extremely complex.Not only because of the penetration of corrosive media,but also seawater impact and high hydrostatic pressure in deep sea,the protection of marine equipment in terms of friction and wear has become a huge challenge.The development of anti-wear coatings in marine environments is of significance for further exploring the marine resources.Epoxy resins（EP）are widely used as corrosion resistant coatings in the of marine environments due to their excellent adhesion properties,chemical stability and simple construction process.However,due to the poor mechanical properties of EP,filler enhancement is critical to increase the tribological performance.Boron nitride possess series of configurations,among which the hardness of cubic boron nitride（CBN）is only second to diamond,and the layered structure of hexagonal boron nitride（HBN）owns outstanding lubricating properties.Both of CBN and HBN are ideal filler materials to improve the tribological performances of EP.Based on the structural regulation of boron nitride/epoxy composite coatings,CBN and HBN enhanced EP composite coatings were prepared.The effects of the structural arrangement of micro/nano CBN and HBN particles in EP on the tribological behaviors of EP coatings were systematically investigated.And the anti-wear and friction reduction mechanism of composite coatings enhanced with HBN-TiO₂ hybrid material was thoroughly explored.First,EP composite coatings reinforced with micro/nano CBN particles（30 wt.%）were prepared,and their tribological and anti-corrosion properties were investigated.The results showed that the surface modification of CBN particles with polydopamine improved their dispersibility and compatibility in epoxy.When the additive proportion of microsized and nanosized CBN was 1:1,the EP composite coating showed the best anti-wear performance under dry tribological conditions.When the additive proportion of microsized and nanosized CBN particles was 2:1,the tribological performance was the best under the condition of seawater lubrication.Micro/nano particle modification brought huge promotion to the mechanical properties of EP,which was the main reason for the improvement of tribological properties.The increase in the hardness of the CBN-EP-2 composite coating was up to 98.0%,and the anti-wear performance under seawater lubrication conditions was positively related to the hardness.When the additive proportion of microsized and nanosized CBN particles was 2:1,the composite coating showed the best corrosion resistance.Microsized and nanosized particles dispersed in EP made the coating structure more compact,improving the mechanical properties of the EP composite coating and enhancing the barrier effect.Secondly,HBN,titanium dioxide（TiO₂）and HBN loaded with TiO₂ nanoparticles（HBN-TiO₂）reinforced EP composite coatings were prepared,and the tribological properties of EP and composite coatings were investigated.The results showed that the mechanical properties of the composite coatings were significantly improved,where the hardness and tensile strength of HBN-TiO₂/EP composite coating were improved by 33.9%and 27.5%,respectively.The addition of TiO₂ nano particles reduced the stress concentration during the friction process,and improved the fatigue resistance of the epoxy composite coating.The addition of two-dimensional material（HBN）realized the lubrication of HBN-TiO₂/EP composite coating through its interlayer self-slip,thereby reducing the friction and wear of the epoxy composite coating.HBN-TiO₂/EP composites displayed significant anti-wear and friction reduction properties and its wear rate was reduced by 65.8%relative to EP,which were attributed to the load carrying capacity of TiO₂ and the self-lubricating effect of HBN nano-sheets,and also the synergistic effect between them.Finally,EP coatings with porous sturcture were prepared by using porous mold,and the lattice distribution of HBN in the EP coatings was realized.The tribological mechanism of HBN/EP composite coating was investigated.The results showed that the porous structure absorbed the energy in the friction process through the generation of cracks,which improved the tribological performance of the EP.The lattice distribution of hexagonal boron nitride effectively reduced the friction coefficient,eliminated the occurrence of cracks,and made the surface wear mode transform to fatigue wear.