Abstract
In the current study, the properties of the CrxN coatings deposited on the Inconel 718 superalloy using direct current reactive magnetron sputtering are investigated. The influence of working pressure on the microstructure, mechanical, and tribological properties of the CrxN coatings before and after high-temperature hydrogen exposure is studied. The cross-sectional scanning electron micrographs indicate the columnar structure of the coatings, which changes from dense and compact columns to large columns with increasing working pressure. The Cr/N ratio increases from 1.4 to 1.9 with increasing working pressure from 300 to 900 mPa, respectively. X-ray diffraction analysis reveals a change from mixed hcp-Cr2N and fcc-CrN structure to approximately stoichiometric Cr2N phase. After gas-phase hydrogenation, the coating deposited at 300 mPa exhibits the lowest hydrogen absorption at 600 °C of all investigated coatings. The results indicate that the dense mixed cubic and hexagonal structure is preferential for hydrogen permeation resistance due to the presence of cubic phase with higher packing density in comparison to the hexagonal structure. After hydrogenation, no changes in phase composition were observed; however, a small amount of hydrogen is accumulated in the coatings. An increase of coating hardness and elastic modulus was observed after hydrogen exposure. Tribological tests reveal that hydrogenation leads to a decrease of the friction coefficient up to 20%–30%. The best value of 0.25 was reached for hydrogen exposed CrxN coating deposited at 300 mPa.
Highlights
Since the commercialization of TiN coatings in 1980s, transition metal nitride hard coatings have been extensively applied in bearings, gears, as well as cutting and forming tools because of their high hardness, good wear, and corrosion resistance [1,2]
Cr–N coatings can be synthesized by various PVD processes, such as hollow cathode discharge [7], pulsed laser deposition [8,9], ion-beam-assisted deposition [10,11], arc ion plating [12,13,14], and magnetron sputtering [15,16,17,18]
Morphology, and mechanical properties of Cr–N coatings deposited using magnetron sputtering strongly depend on the deposition parameters, such as working pressure, bias voltage, substrate temperature, target power, substrate frequency, nitrogen flow rate, etc. [4,18,19,20,21]
Summary
Since the commercialization of TiN coatings in 1980s, transition metal nitride hard coatings have been extensively applied in bearings, gears, as well as cutting and forming tools because of their high hardness, good wear, and corrosion resistance [1,2]. Their capability to extend tool lifetime in abrasive and corrosive environments has been verified [3]. Morphology, and mechanical properties of Cr–N coatings deposited using magnetron sputtering strongly depend on the deposition parameters, such as working pressure, bias voltage, substrate temperature, target power, substrate frequency, nitrogen flow rate, etc. Cr–N coatings can be synthesized by various PVD processes, such as hollow cathode discharge [7], pulsed laser deposition [8,9], ion-beam-assisted deposition [10,11], arc ion plating [12,13,14], and magnetron sputtering [15,16,17,18].
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