Mechanical properties of nanocrystalline Ti-B-(N) coatings produced by DC magnetron sputtering

Ti-B-(N) coatings have been deposited by DC magnetron sputtering using TiB2 targets in Ar/N-2 gas mixtures. The influence of bias voltage and nitrogen flow on the mechanical and tribological properties of these coatings has been studied. Mechanical properties have been evaluated by ultra-microindentation techniques and scratch testing; tribology tests have been performed in a pin-on-disc apparatus with controlled humidity conditions. Microstructural characterization by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) demonstrates the nanocrystalline structure of Ti-B-(N) coatings and allows the interpretation of their mechanical behaviour. Hardness values up to 58 GPa have been achieved, depending on deposition conditions. Increasing the bias voltage on the substrates improves the hardness of coatings, while the addition of nitrogen significantly decreases these values. Coating adhesion obtained on highspeed steel is very good in most cases, reaching values higher than 60 N of critical load. Tribotests performed on these coatings against a steel contact (wear conditions: 0.98 N load, 10 cm/s, 50% RH, 10 mm bearing steel ball diameter) have yielded very low wear rates but friction coefficients in the range of 0.6-1.0. (c) 2005 Elsevier B.V. All rights reserved.