Structure, Mechanical and Tribological Properties of MoSN/MoS2 Multilayer Films

Abstract

MoSN/MoS2 multilayer films were deposited by a sputtering MoS2 target in alternate Ar and Ar/N2 mixed atmospheres with different nitrogen flow rates. The influence of nitrogen flow rates on the microstructure, mechanical and tribological properties of the prepared films were investigated. The multilayer film exhibited the preferred orientation of (002) plane for MoS2 sublayers and amorphous structure for MoSN sublayers. Introducing N2 into the source gas resulted in a much more compact structure for multilayer films due to the suppression of columnar growth of MoS2 film. With the increase of the nitrogen flow rate, the hardness of the multilayer film firstly increased from 2.3 to 10.5 GPa as the nitrogen flow rate increased from 4 to 10 sccm and then turned downwards to 6.5 GPa at 20 sccm. MoSN/MoS2 film deposited with an optimized microstructure exhibited low friction coefficients below 0.03 and a wear life higher than 1.8×105 revolutions in vacuum. Meanwhile, the optimized film showed an ultralow friction coefficient of 0.004~0.01 and wear rate of 4.7 × 10−7 mm3/N·m in an ultrahigh vacuum. Both the enhanced hardness by N-doping and sustainable formed MoS2 tribofilm contributed to the improved tribological property of MoSN/MoS2 multilayer film.

Mechanical Properties and Vacuum Tribological Performance of Mo–S–N Sputtered Coatings

“…Similar observations were reported in the literature for other multilayer materials, for example, for WS 2 /MoS 2 and TiN/VN coatings. Despite the higher S/Mo ratio and then a higher amount of the MoS 2 soft phase, the synergy of the factors mentioned above allows us to provide hardness values higher than those found in the literature. ,,, …”

“…Despite the higher S/Mo ratio and then a higher amount of the MoS 2 soft phase, the synergy of the factors mentioned above allows us to provide hardness values higher than those found in the literature. 26,31,40,46 The detailed vacuum tribological studies were carried out under different conditions of applied loads and mating surfaces. For the first time, Mo−S−N coatings were tested with contact stresses complying with real industrial requirements.…”

“…This choice of low contact stresses is in contrast to most of the literature, where solid lubricants are tested under much higher applied contact stresses in the range 500–1500 MPa. Thus, the COF reported in the current study would simulate the values during real applications, unlike those in literature. ,,, Different mating conditions were tested as the initial state of mating materials can affect the COF values. It was found that the sliding of coatings with itself (i.e., coated cylinder versus coated flat) provided a short running-in period and a stable COF if compared to the condition where one surface is uncoated.…”

“…Additionally, most of the Mo−S−N coatings were only studied in dry N 2 and humid air conditions. The vacuum tribology of this system has not been reported except for the work of Fu et al 46 and Zhang et al 31 Again, in these works, tests were conducted at much higher applied contact stresses (∼1500 MPa and ∼950 MPa), which is not a realistic approach for applications such as those existing in space industries/components. Thus, this current work deals with vacuum tribology of optimized Mo−S−N coatings in low contact stress regime, so that the results can considerably be more practical and reliable for industrial implementation, especially for space applications.…”

“…Additionally, most of the Mo–S–N coatings were only studied in dry N 2 and humid air conditions. The vacuum tribology of this system has not been reported except for the work of Fu et al and Zhang et al Again, in these works, tests were conducted at much higher applied contact stresses (∼1500 MPa and ∼950 MPa), which is not a realistic approach for applications such as those existing in space industries/components.…”