Combined steered cathodic arc/unbalanced magnetron grown C/Cr nanoscale multilayer coatings for tribological applications

Abstract

C/Cr nano-scale multilayer coatings have been produced by the combined steered cathodic arc/unbalanced magnetron sputtering technique. The coating was deposited by non-reactive unbalanced magnetron sputtering from three graphite targets and one chromium target at deposition temperatures of 250, 350 and 450 °C. In scratch adhesion tests C/Cr coatings deposited on M2 HSS showed values exceeding critical load of 70 N. The XRD and TEM analysis revealed the amorphous nature of the coatings. Higher deposition temperatures led to an increase in crystallinity. Raman spectroscopy also showed that the amount of the carbon disorder depends on the deposition temperature, increasing from 68 to 86% for deposition temperatures of 250 and 450 °C, respectively. In pin-on-disc tests, C/Cr coatings exhibit a low coefficient of friction of between 0.1 and 0.2, when sliding against 100Cr6 steel ball. These low values were retained for tests in air, de-ionised water and engine oil. Remarkably low sliding wear coefficients of 2×10 −17 m 3/Nm for the coating and 1×10 −19 m 3/Nm for the counterpart were measured after 22.6 km sliding distance. However, the increased crystallinity of the coatings produced at higher deposition temperature leads to an increase in the friction coefficient. The C/Cr coatings, used as an overcoat on TiAlCrYN coated cemented carbide end mills, led to reduction of the rake and the flank wear rates by factor of 7 when machining extremely abrasive Ni based alloys.