Study of the tribological properties of MoN cathodic arc coatings applied to steel

DOI: 10.62564/M4-VP1632

Viktoriya Podhurska¹, Illya Klimenko², Vitaliy Belous², Orest Ostash¹, Valeriy Ovcharenko², Galyna Tolmachova², Igor Kolodiy², Mykhailo Ishchenko³, Ivan Babayev³, Oleksandr Kuprin<sup>2

1</sup>Karpenko Physico-Mechanical Institute of the NAS of Ukraine
²National Science Center Kharkiv Institute of Physics and Technology, Ukraine
³JSC “Ukrainian Energy Machines”, Ukraine


The molybdenum nitride coating deposited by the vacuum arc method was one of the first coatings to be used for the protection of machine tools and machine parts. The vacuum arc method allows the deposition of molybdenum nitride with different stoichiometry and crystalline phases of cubic γ-Mo₂N and hexagonal δ-MoN. The binary system of Mo–N offer a high potential to enhance the tribological properties of common hard coatings, owing to their ability to form lubricious oxides (Magnéli phases) at elevated temperatures. However, the application of Mo-N coatings at high temperatures is limited to 500°C [1]. The work aim is to investigate the effect of deposition process parameters (bias voltage), tribopair Al₂O₃, ShKh15 steel, ShKh15 steel with CrN, TiN and MoN coatings and test temperature on the tribological properties of MoN coatings deposited by cathodic arc evaporation method on 15Х12ВНМФ steel. In all coatings deposited on steel at a nitrogen pressure of 0.3 Pa and bias potentials (-30, -50 and -70 V), hexagonal molybdenum nitride δ-MoN was found. The nanohardness of the deposited coatings is at the level of 34.1...34.7 GPa, and the Young's modulus is 437...471 GPa. The MoN coating on the steel substrate is characterized by low wear at the level of 1.57-2.43·10⁻⁵ mm³/Nm at room temperature tests. An increase in the test temperature to 500 °С leads to a significant (by an order of magnitude) increase in the wear coefficient of 1.83-2.17·10⁻⁴ mm³/Nm. This is due to the low resistance of molybdenum nitride to oxidation at this temperature. Molybdenum nitride oxidizes to molybdenum oxide, which can lead to rapid degradation of the coating under load. The lowest coefficient of friction for the MoN coating was recorded in a pair with a TiN-coated steel ball (0.37), and the lowest wear (10⁻⁷ mm³/N·m) for the MoN – steel and MoN – TiN pairs.

Keywords
Molybdenum nitride, structure, nanohardness, friction coefficient, wear

Acknowledgments
The work was financially supported by the National Academy of Science of Ukraine (program “Support of the development of main lines of scientific investigations” (KPKVK 6541230))

References
[1] H. Hazar, Characterization of MoN coatings for pistons in a diesel engine, Materials and Design, 2010. V.31, No.1. P. 624–627.