TITANIUM BORON-NITRIDE COATINGS OF VERY HIGH HARDNESS

Ti-B-N coatings of variable composition have been sputter deposited fr om a heterogeneously composed Ti-BN target, consisting of a boron nitr ide base plate on which small Ti platelets were regularly arranged. By varying the number of platelets the concentration ratio C-Ti/C-B of t he target and therefore also of the coating could easily be varied. In homogeneities in the chemical composition were in the per cent range. Very hard coatings of up to 55 GPa were obtained by sputtering with a substrate bias of -150 V at a substrate temperature of 400 degrees C. The hardness maximum was found at a chemical composition where both th e TiB2 and the TiN phases coexist in equal concentrations. All coating s show very broad diffraction peaks indicating average grain sizes in the nanometre range where the Hall-Fetch relation is no more valid. Wi th coatings composed of very small grains an inverse Hall-Fetch effect was observed. The tribological performance of the Ti-B-N coatings is promising; however, in general it is worse than that observed with TiN coatings. The main reason seems to be the relatively low cohesive str ength of the material.