Abstract
In this study, Mo-Cu-V-N composite coatings with high Cu content of ~18 at.% were deposited on 316L stainless steel and YT14 cemented carbide substrates by high power impulse magnetron sputtering in Ar–N2 gas mixtures. The influence of N2 partial pressure was investigated with respect to the microstructure and tribological properties of the coatings. The results indicated that the Mo-Cu-V-N composite coatings exhibited FCC B1-MoN phase with a strong (200) preferred orientation, and Cu phase was found to exist as metallic species. As the N2 partial pressure increased from 0.11 to 0.35 Pa, the peak intensity of (200) plane decreased gradually and simultaneous peak broadening was observed, which was typical for grain refinement. With increasing the N2 partial pressure, the columnar microstructure became much coarser, which led to the decrease of residual stress and hardness. The Mo-Cu-V-N composite coatings with high Cu content exhibited a relatively low wear rate of 10−8 mm3/N·m at 25 °C, which was believed to be attributed to the mixed lubricious oxides of MoO2, CuO and V2O5 formed during tribo-oxidation, which cannot be formed in the coatings with low Cu content. When the wear temperature was increased up to 400 °C, the wear rate increased sharply up to 10−6 mm3/N·m despite the formation of lubricious oxides of MoO3/CuMoO4 and V2O5. This could be due to the loss of nitrogen and pronounced oxidation at high temperatures, which led the wear mechanism to be transformed from mild oxidation wear to severe oxidation wear.
Highlights
In the last decade, solid lubricants have been developed to achieve favorable abrasion resistance and good lubricating capability in various tribological applications [1,2,3]
The aim of this work is to prepare the Mo-Cu-V-N composite coatings with high Cu content to further investigate the influence of N2 partial pressure on the microstructure, residual stress and tribological properties, and to find out the wear mechanism of the self-lubricating coatings at elevated temperatures up to 400 ◦ C
Composite coatings with high Cu content of ~18 at.% deposited at various N2 partial pressures were investigated
Summary
Solid lubricants have been developed to achieve favorable abrasion resistance and good lubricating capability in various tribological applications [1,2,3]. The tribological effectiveness of solid lubricants often begins to fail due to the thermal degradation or oxidation at elevated temperatures [4,5,6]. Some lubricious materials at elevated temperatures have been investigated by using oxide materials. These lubricious oxides are often referred to as Magnéli phases, which usually shows easy crystallographic shear planes, good oxidation stability and excellent tribological properties [7]. The self-lubricating effect is based on the formation of lubricious oxides of MoO3 [8,9,10] and V2 O5 [11,12,13]. Some soft metals possess lubrication properties due to their low shear strength and high plasticity. Multi-functional self-lubricating coatings can be obtained by the addition of these alloying elements
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