Effects of deposition parameters on hardness and lubrication properties of thin MoS₂ films

Abstract

The purpose of the present study is the development of a sputtered MoS2‐coating suitable for the use in humid atmospheres. Influences of the process parameters argon pressure, temperature, distance between substrate and target and bias voltage on tribological properties and hardness are presented. By means of these parameter studies, different microstructures with widely varying wear behavior were achieved. Life cycle tests show that exclusively basal oriented coatings with dense, non columnar structures show the highest durability and a hardness of about 400 HV 0.01. However, dendritic needle like structures show lower endurance and lower hardness (<100 HV 0.01). Films with a comparatively high hardness (up to 800 HV 0.01) exhibit lowest sliding distances until failure due to an appearance of spalling in the ball‐on‐disc tests. Those coatings also show a dense but amorphous structure and sulfur deficiencies. Consolidation during sputtering, i. e. film hardness and porosity, can be controlled by certain process parameters and is probably affected by varying amounts of internal stress.

Strength measurement and rupture mechanisms of a micron thick nanocrystalline MoS2 coating using AFM based micro-bending tests

“…The mechanical characterization conducted in the present study plays a key role in better understanding the tribological behavior of this lubricant. The noted nanocrystalline structure aids in explaining why this lubricant performs better than purely amorphous coatings [1] or much harder coatings (H=8 GPa) [15]. The present study demonstrates that the coating can resist compressive stresses more than tensile stresses as the nanocrystalline network and porosities deter crack propagation throughout in the bulk under compression.…”

“…Regarding the hardness, the static nanoindentation results present a medium-high hardness value of 4.0 GPa compared to 0.5-8 GPa for MoS2 coatings in literature [10][11][12][13][14][15][16]. This is likely due to the nanocrystalline structure of the coating in accordance with the Hall-Petch effect [57]; the high concentration of grain boundaries in nanocrystalline materials inhibit dislocation movement which provides a material with high hardness and low ductility [58].…”

“…This particular MoS2 coating has been previously described as a dense columnar-like nanocrystalline structure (fibrous and vertically oriented) [36] based on the cauliflower aspect of its surface, the deposition parameters, and fractured surfaces of delaminated portions [15,[36][37][38][39].…”

“…This deposition variability directly influences the structure of MoS2 coatings; ranging from highly organized columnar structures [6] to fully amorphous structures [10]. Studies on the mechanical properties of MoS2 coatings also demonstrate a wide variance with Young's modulus and hardness values ranging from 50 to 170 GPa [3,[10][11][12] and from 0.5 to 8 GPa [3,[10][11][12][13][14][15][16] respectively. Furthermore, there is a limited number of studies on both the rupture and the fracture strength of the coatings.…”

Empirical-Statistical Study on the Relationship between Deposition Parameters, Process Variables, Deposition Rate and Mechanical Properties of a-C:H:W Coatings

“…The a-C:H:W coatings were deposited using an industrial-scale coating machine, H-O-T TT 300, described elsewhere [26], with a three-fold rotating charging rack. Prior to coating deposition, the specimens were ultra-sonically cleaned in acetone and isopropanol, dried using nitrogen and plasma etched inside the coating machine.…”