Hard tribological Ti–Cr–B–N coatings with enhanced thermal stability, corrosion- and oxidation resistance

Corrosion and oxidation resistance are of great importance for hard tribological coatings when it concerns thermal stability under severe cutting conditions. A comparative investigation of Cr-doped Ti–B–N coatings deposited by DC magnetron sputtering of TiCrB targets with 20, 30 and 40 wt.% of chromium in a gaseous mixture of argon and nitrogen is presented. The TiCrB composite targets were synthesized using combined force SHS-pressing technology. The structure, elemental and phase composition were studied by means of X-ray diffraction, transmission and scanning electron microscopy, as well as focused ion beam equipped with secondary ion mass spectrometer. To evaluate the thermal stability and oxidation resistance, the Ti–Cr–B–N coatings were annealed at 600, 800, and 1000 °C in vacuum and at 600, 700, 800, and 900 °C in air, respectively. The potentiodynamic polarization tests of the Ti–Cr–B–N coatings were carried out and compared with those for the Ti–B–N, Ti–Si–B–N, and Ti–Al–Si–B–N reference coatings. From the results obtained it can be concluded that the magnetron sputtering of TiCrB composite targets under controlled deposition parameters resulted in the growth of strongly (100) textured Ti–Cr–B–N coatings with high hardness and wear resistance, superior thermal stability up to 1000 °C, improved oxidation resistance up to 900 °C, and enhanced corrosion resistance in 1 N H2SO4 solution.