NANOSTRUCTURED TITANIUM BORON-NITRIDE COATINGS OF VERY HIGH HARDNESS

The interest in Ti-B-N coatings arises from the fact that they generally are composed of several phases. Multiphase systems display many similarities with composite materials and often display higher hardness and toughness values than single-phase materials. Ti-B-N coatings of different composition have been prepared by sputter deposition from composite Ti/BN targets at a substrate temperature of 20 degrees C. The coatings were characterized by scanning electron microscopy, glancing angle X-ray diffraction and by X-ray photoelectron spectroscopy and Anger electron spectroscopy. The hardness and elasticity were determined by nanoindentation. All films had a dense structureless morphology. The highest hardness and elasticity were obtained with coatings of composition TiBN0.5. Annealing at 400 degrees C for up to 6 h produced a 40%-50% hardness and elasticity increase, The origin of this increase could not be attributed to a detectable change in grain size or phase composition. The grain size of the films was of the order of 2 nm. In spite of the high quenching rates associated with sputter deposition, the films were found to contain the phases which are expected to occur under equilibrium conditions according to the phase diagram of the ternary Ti-B-N system.