Abstract
The production of tribological nanoscale multilayer CrN/NbN coatings up to 6 µm thick by Sputtering/HIPIMS has been reported in literature. However, high demanding applications, such as internal combustion engine parts, need thicker coatings (>30 µm). The production of such parts by sputtering would be economically restrictive due to low deposition rates. In this work, nanoscale multilayer CrN/NbN coatings were produced in a high-deposition rate, industrial-size, Cathodic Arc Physical Vapor Deposition (ARC-PVD) chamber, containing three cathodes in alternate positions (Cr/Nb/Cr). Four 30 µm thick NbN/CrN multilayer coatings with different periodicities (20, 10, 7.5 and 4 nm) were produced. The coatings were characterized by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The multilayer coating system was composed of alternate cubic rock-salt CrN and NbN layers, coherently strained due to lattice mismatch. The film grew with columnar morphology through the entire stratified structure. The periodicities adopted were maintained throughout the entire coating. The 20 nm periodicity coating showed separate NbN and CrN peaks in the XRD patterns, while for the lower periodicity (≤10nm) coatings, just one intermediate lattice (d-spacing) was detected. An almost linear increase of hardness with decreasing bilayer period indicates that interfacial effects can dominate the hardening mechanisms.
Highlights
The chromium nitride (CrN) is a classic coating system, which is technologically relevant since the early 1980’s1-5
The results showed that the position of CrN and NbN X-ray diffraction peaks represented the weighted mean of the individual reflections of the CrN and NbN phases
Chromium-based hard coatings produced by PVD have been used successfully in tribological systems where corrosion, oxidation and intense wear are expected
Summary
The CrN is a classic coating system, which is technologically relevant since the early 1980’s1-5. The high hardness and lower friction coefficient, when compared to other piston ring system coatings[2,6,7], has drawn engineer’s attention to the use of this kind of coating for internal combustion engine components. It is applied in large scale for piston rings[2,5]. While typical applications may not require the PVD coating thickness to be above 6 μm 5, it frequently needs to be on the order of 30 μm when the PVD layer is deposited onto a combustion engine component[5,6,7]. The increasing combustion pressures and the reduced lubrication oil availability found in new generation engines require additional toughness and wear resistance to avoid damage of the parts
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