High temperature tribology of CrN and multilayered Cr/CrN coatings

Chromium nitride (CrN) and multilayers Cr/CrN coatings were deposited by low cathodic arc technology. The thickness of Cr and CrN layers was identical; two different multilayer coatings were deposited with layer thicknesses of 85 and 160 nm. The structural analysis showed that CrN coatings exhibited the cubic CrN phase, while a mixture of CrN, Cr2N and Cr phases was observed in the case of multilayers. The annealing of the samples at 800 and 900 °C in air led to: (1) the decomposition of the chromium nitride phases into chromium; (2) a moderate oxidation by forming a thin Cr2O3 layer on the coating surface and, (3) carbon diffusion from the steel substrate. The chemical composition depth analysis performed by glow discharge optical emission spectroscopy (GDOES) showed a nitrogen-rich layer below the surface oxide layer for Cr/CrN multilayers. The multilayer structure, clearly visible by GDOES at room temperature, disappeared at 800 °C. Friction and wear analysis carried out by pin-on-disc in the temperature range 600–800 °C followed by the wear track observation by scanning electron microscopy showed that the dominant feature influencing the tribological properties was the formation of a tribolayer. The tribolayer consisted of small wear debris particles of chromium oxide pressed together and well adhered in the wear track. The multilayer Cr/CrN coatings showed a slightly better wear resistance than CrN film.