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Boron nitrogen carbide coatings for wear resistant applications

Plasma assisted chemical vapour deposition (PACVD) proved to be a very flexible technique for growing amorphous films over a wide range of the boron nitrogen carbide triangles. The hardest films were obtained at the powered electrode. The pure boron and carbon films had nearly identical and relatively high hardness values. The diamond-like carbon films had the best wear resistant properties combined with a low friction coefficient under unlubricated sliding. Adding nitrogen or boron to diamond-like carbon films reduced the hardness and wear resistance but were beneficial for the resilience of the coatings, thereby improving their adhesion properties. Fully stoichiometric and transparent a-baron nitrogen:hydrogen films with relatively high hardness could be deposited. Application-oriented evaluation showed that the adhesion of these coatings depended strongly of the hardness of the substrate. Tribological simulations under engine conditions proved the wear resistance together with a low friction coefficient.

Regarding the formation of boron-carbon based coatings by laser induced chemical vapour deposition (LCVD), a complete scanning of the gas phase composition and laser parameters led to the deposition of rhombohedric boron carbide, tetragonal boron carbide, graphite and several mixtures of these phases on fused silica. The deposition of pure boron carbide films, with high hardness, good adhesion and structural and chemical properties was achieved at low and atmospheric pressure. Addition of ethane allowed a full exploitation across the composition triangle. Dimethylamine (DMA) was tested as a simultaneous carrier for carbon and nitrogen, giving coatings with hardness values up to 40 GPa. Deposition by means of magnetron sputtering ion plating has been checked by applying three types of targets (hexagonal boron nitride, boron carbide and graphite), showing three interesting areas for future industrial evaluation. In spite of the high hardness and internal stresses, reliable adhesion for the super hard boron carbon films was obtained on aluminium alloys followed by high speed steel (HSS)-substrate and 100Cr6.

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