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

Yanlong Fu,Bo Mu,Xianjuan Pang,Wu Yang,Tengfei He,Jiao Xu,Peng Wang

doi:10.3390/coatings9020108

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.

Highlights

Transition metal dichalcogenides (TMDs), typically MoS2 and WS2, are well known as excellent solid lubricants due to the weak van der Waals interactions between basal planes [1,2,3,4,5], which allows for an easy shearing along the direction parallel to the sheets and thereby, leading to low friction coefficients in vacuum and dry inert atmospheres [4]
The MoSN/MoS2 multilayer films were deposited by r.f. sputtering the MoS2 target with a power of 275 W under a working pressure of 0.75 Pa controlled by a constant Ar flow rate of 40 sccm and different N2 flow rates of 4, 6, 10, and 20 sccm, respectively
The prepared MoSN/MoS2 multilayer films were denoted as N4, N6, N10 and N20 films corresponding to the N2 flow rates of 4, 6, 10, and 20 sccm, respectively

Summary

Introduction

Transition metal dichalcogenides (TMDs), typically MoS2 and WS2 , are well known as excellent solid lubricants due to the weak van der Waals interactions between basal planes [1,2,3,4,5], which allows for an easy shearing along the direction parallel to the sheets and thereby, leading to low friction coefficients in vacuum and dry inert atmospheres [4]. Sputtering-deposited MoS2 films generally exhibit porous structure, low hardness, low-bearing capacity, and high wear rate [6,7,8,9,10]. Some methods have been developed to date to improve the density, hardness and tribological properties of sputtered TMDs films, either by doping with other elements [5,6,7,10,11,12,13,14,15] or fabricating multilayered structures such as. It has been investigated that the doped MoS2 film with the optimum doping level of Cr or Ti showed both a low friction coefficient and wear rate even in moist atmosphere [10]. Non-metallic elements, especially nitrogen and carbon, Coatings 2019, 9, 108; doi:10.3390/coatings9020108 www.mdpi.com/journal/coatings

Methods

Results

Conclusion