Abstract
Within this study, self-lubricating and triboactive (Cr,Al)N+Mo:S coatings were developed and investigated for the deposition on components in a low-temperature physical vapor deposition (PVD) hybrid process. Therefore, direct current magnetron sputtering (dcMS) and high power pulse magnetron sputtering (HPPMS) PVD were combined by using an industrial coating machine. Hereby, it was possible to deposit dense and smooth triboactive, self-lubricating nitride coatings with different chemical compositions and architectures on 16MnCr5E samples. Two coating architectures, a matrix monolayer and a graded coating structure, were developed to evaluate the effect on the tribological behavior. The morphology and coating thickness were analyzed by means of scanning electron microscopy (SEM). Furthermore, the indentation hardness and modulus of indentation as well as the compound adhesion between substrate materials and coating were analyzed. Tribological analyses of (Cr,Al)N+Mo:S-coated and uncoated samples were conducted under fluid-free friction regime at room temperature T = (20 ± 3) °C, a velocity v = 0.1 m/s and a distance s = 1000 m by varying the Hertzian contact pressure from 400 MPa ≤ pH ≤ 1300 MPa against steel counterparts, 100Cr6, in a pin-on-disk (PoD) tribometer. The graded coating architecture of (Cr,Al)N+Mo:S enabled a significant wear and friction reduction. Furthermore, Raman analyses prove the formation of solid lubrication tribofilm containing MoS2, MoO3 MoO2 and MoxOy at the toplayer of a graded (Cr,Al)N+Mo:S coating, which are responsible for the improved tribological behavior.
Highlights
Today, gearboxes are conventionally lubricated with greases or oils
Direct current magnetron sputtering and high power pulse magnetron sputtering (HPPMS) physical vapor deposition (PVD) were combined by using an industrial coating machine
The in situ temperature measurement system proves that high HPPMS cathode power up to P=5000 W has a neglectable effect on the substrate temperature of the 16MnCr5E samples
Summary
Gearboxes are conventionally lubricated with greases or oils. mineral oil or synthetic oilbased lubricants are often not applicable in medical technology, food technology, production under vacuum processes technology and aerospace applications due to extreme ambient conditions. Within the scope of this study, the goal was to investigate the effect of two different coating architectures on friction reduction by the solid lubricant MoS2 and increased wear resistance through the use of (Cr,Al)N For this purpose, the two coating architecture concepts (i) matrix and (ii) graded (Cr,Al)N coating with a nitride-based toplayer and embedded Mo and S were developed and analyzed. The idea of the monolayer matrix coating was to produce a coating with a constant depot of embedded Mo and S depots from the intermediate layer to the toplayer This should enable the in situ formation of the solid lubricant MoS2 during the tribological contact, Fig. 2a. Tribological tests were conducted at fluid-free friction regime in a steel/steel and coating/ steel contact at different initial Hertzian pressure pH= 400 MPa, pH=600 MPa, pH=800 MPa and pH= 1300 MPa calculated based on basic part and counterpart properties. The laser was calibrated before the measurement by using a silicon reference sample
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