Minimizing friction and wear is one
of the continuing challenges
in many mechanical industries. Recent research efforts have been focused
on accelerating the antifriction and antiwear properties of hard coatings
through the incorporation of self-lubricant materials or the development
of new architectures. In this present study, carbon-rich MoC, MoCN,
and multilayer MoC/MoCN coatings were deposited using reactive magnetron
sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy
(XPS), and Raman spectroscopy were used to evaluate their properties,
which revealed the presence of ceramic cubic crystallites, covalent
bonds between primary elements, and an excess of amorphous carbon
(a-C) in all of the coatings. The multilayer architecture and possible
segregation of a-C around the ceramic crystallites resulted in improved
mechanical properties for all coatings, with MoC/MoCN coatings having
a maximum hardness of 21 GPa and elastic modulus of 236 GPa. Friction
and wear behavior are initially determined by the structural–composition–property
relationships of the respective coatings; later, the tribological
characteristics are altered depending on the nature of tribolayer
on both mating surfaces at the contact interface. The highest wear
resistance of multilayer MoC/MoCN coating (8.7 × 10–8 mm3/N m) and MoC coating (3.9 × 10–7 mm3/N m) was due to the dissipation of contact
stress by the tribofilm consisting of carbon tribo products like graphitic
sp2 carbon, diamond-like sp3 carbon, and pyrrolic-N.
On the other hand, MoCN coating depicted a lower wear resistance due
to the frequent termination of C–H bonds by N, which restricts
the strong formation of tribofilms as well as poor mechanical properties.