Structural, mechanical and tribological properties of Mo–S–N solid lubricant films

• The Mo-S-N films were deposited by magnetron sputtering in N2 atmosphere.
• Sputter-deposited Mo–S–N films of different composition and structure were studied.
• The mechanical properties of the Mo-S-N films can be enhanced dramatically due to the addition of N.
• Properly prepared Mo-S-N films exhibit low friction and wear rate in a vacuum condition.

In this paper, the composite Mo-S-N solid lubricant films are synthesized by magnetron sputtering of molybdenum disulphide (MoS2) target in nitrogen and argon atmosphere. With the increase of the nitrogen content, the nitrogen concentration in the deposited films increases from 0 to 35 at.%, and the corresponding S/Mo atomic ratio reduces to below 0.70. X-ray diffraction (XRD) and Raman spectroscopy analyses reveal that introducing nitrogen into films leads to the formation of amorphous structure and chemical bonds between nitrogen and molybdenum were detected by X-ray photoelectron spectroscopy. The hardness and elastic modulus of Mo–S–N films increase more than one order of magnitude higher than that of pure MoS2 films with increasing the N2 flow rate (i.e., with increasing N content), reaching to the maximum of 9.59 and 113.12 GPa, respectively. The tribological properties of the prepared films tested by a ball-on-disc tribometer under a low-pressure vacuum exhibit that the incorporation of a suitable content of N dopant could significantly reduce the wear rate, however, both friction coefficient and wear rate increase dramatically in excess a certain amount of N dopant.