Abstract
The coatings ZrB2 and Zr-B-N were deposited by magnetron sputtering of ZrB2 target in Ar and Ar–15%N2 atmospheres. The structure and properties of the coatings were investigated via scanning and transmission electron microscopy, energy dispersion analysis, optical profilometry, glowing discharge optical emission spectroscopy and X-ray diffraction analysis. Mechanical and tribological properties of the coatings were investigated using nanoindentation, “pin-on-disc” tribological testing and “ball-on-plate” impact testing. Free corrosion potential and corrosion current density were measured by electrochemical testing in 1 N H2SO4 and 3.5%NaCl solutions. The oxidation resistance of the coatings was investigated in the 600–800 °C temperature interval. The coatings deposited in Ar contained 4–11 nm grains of the h-ZrB2 phase along with free boron. Nitrogen-containing coatings consisted of finer crystals (1–4 nm) of h-ZrB2, separated by interlayers of amorphous a-BN. Both types of coatings featured hardness of 22–23 GPa; however, the introduction of nitrogen decreased the coating’s elastic modulus from 342 to 266 GPa and increased the elastic recovery from 62 to 72%, which enhanced the wear resistance of the coatings. N-doped coatings demonstrated a relatively low friction coefficient of 0.4 and a specific wear rate of ~1.3 × 10−6 mm3N−1m−1. Electrochemical investigations revealed that the introduction of nitrogen into the coatings resulted in the decrease of corrosion current density in 3.5% NaCl and 1 N H2SO4 solution up to 3.5 and 5 times, correspondingly. The superior corrosion resistance of Zr-B-N coatings was related to the finer grains size and increased volume of the BN phase. The samples ZrB2 and Zr-B-N resisted oxidation at 600 °C. N-free coatings resisted oxidation (up to 800 °C) and the diffusion of metallic elements from the substrate better. In contrast, Zr-B-N coatings experienced total oxidation and formed loose oxide layers, which could be easily removed from the substrate.
Highlights
Introduction iationsThe borides of transitional metals are prospective candidates for protective coatings for machining tools [1], heavy-duty friction couplings [2], fuel cells [3], aerospace vehicles [4], etc., due to the inherent high hardness, resistance towards corrosion, high-temperature oxidation and wear, high diffusion-barrier properties and low friction coefficient
The introduction of nitrogen in the composition of the boride coatings opens the opportunity for the formation of nanocomposite structure comprised of nanosized crystals of borides or nitrides of transitional metals and amorphous boron nitride-based interlayers
This work aimed to conduct a comparative study of the structure, mechanical properties, tribological performance and corrosion resistance in aggressive gaseous and liquid media for two types of coatings deposited in Ar and Ar + 15%N2 atmosphere by magnetron sputtering of a ZrB2 target
Summary
The borides of transitional metals are prospective candidates for protective coatings for machining tools [1], heavy-duty friction couplings [2], fuel cells [3], aerospace vehicles [4], etc., due to the inherent high hardness, resistance towards corrosion, high-temperature oxidation and wear, high diffusion-barrier properties and low friction coefficient. The introduction of nitrogen in the composition of the boride coatings opens the opportunity for the formation of nanocomposite structure comprised of nanosized crystals of borides or nitrides of transitional metals and amorphous boron nitride-based interlayers. Such structures display a unique combination of hardness up to 40 GPa, 70–90% elastic recovery, phase stability and oxidation resistance up to 900–1000 ◦ C [13].
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