Tribological behavior of thick CrN coatings deposited by modulated pulsed power magnetron sputtering

Abstract

Thick CrN coatings (up to 55 μm) have been deposited on different substrate materials (WC–Co, M2 steel, AISI 440C steel, AISI 304 steel, Al–Si eutectic alloy, and copper) using the modulated pulsed power (MPP) magnetron sputtering technique at a high deposition rate of 10 μm/h. The thick CrN coatings have been characterized for the microstructure, mechanical and tribological properties. The adhesion of the coatings with different thicknesses on different substrates was evaluated using progressive scratch tests. The dry sliding wear tests for the thick coatings deposited on the AISI 440C substrate were carried out using a ball-on-disk microtribometer. The wear tests were conducted on the 20 μm thick MPP CrN coatings using different ball materials (α-Al 2O 3, WC–Co, AISI 440C steel, AISI 302 steel, 100Cr6 steel, and brass), different applied loads (5–40 N) and sliding speeds (5–50 cm/s) for a maximum sliding distance up to 10 km. The coating wear tracks and ball wear scars were examined using scanning electron microscopy. The thick CrN coatings showed coefficients of friction in the range of 0.48–0.94 as sliding against different materials and under different test conditions. The wear rate of the coatings increased with the increases in the applied load and sliding speed, which is related to an increase in the plowing force (plastic deformation of the substrate) and an increase in the flash temperature, respectively. The wear rates of the 20 μm thick MPP CrN coating are in the range of 1 × 10 − 7 to 5.5 × 10 − 7 mm 3 N − 1 m − 1 . This study has demonstrated that thicker CrN coatings exhibited larger load and sliding speed capacities, which allow them to be operated under more severe conditions, e.g. higher loads, sliding speeds, and operating temperatures.