Wear behavior of as-deposited and oxidized ternary (Zr,Hf)N coatings
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I. INTRODUCTION
THIN ceramic coatings are widely used to improve the service life and tribological performance of cutting and forming tools because of their superior physical, chemical, and mechanical properties.[1–4] Increasing demands for improved wear and corrosion resistance have triggered the further development of these coatings. Today, besides binary nitrides such as TiN, ZrN, and HfN,[5–11] multicomponent and multiphase coatings—binary nitrides alloyed with a third element such as (Ti,Zr)N, (Ti,Hf)N, and (Ti,Al)N—are of increasing interest as protective coating systems. Since most cutting and forming tools are exposed to heavy oxidation during operation, the oxidation behavior of thin ceramic coatings seems to be an important property to consider. Previously,[12–18] the effect of oxidation on the surface properties of various binary (TiN, ZrN, and CrN) and ternary ((Ti,Zr)N, (Ti,Al)N, and (Ti,Cr)N) coatings has been systematically examined. However, tribological studies on the performance of oxidized thin ceramic coatings are scarce. The present study examines the mechanical properties and tribological performance of a commercially available binary ZrN coating and a ternary (Zr,Hf)N coating in the asdeposited and oxidized conditions.
on the substrates using the Zr and Zr 21 pct Hf cathodes. (Zr,7 pct Hf)N was deposited by using two Zr and one Zr 21 pct Hf cathodes. In the case of (Zr,12 pct Hf)N coating, one Zr and one Zr 21 pct Hf cathode were used. After the coating process, samples were isothermally annealed in an air-circulating furnace at 400 °C for times up to 12 hours, interrupted at 2-hour intervals to determine the mass gain of the samples and characteristics of the coatings. Mass gain was determined by using an electronic balance with an accuracy of 0.1 mg. In this study, the oxidation temperature of 400 °C was selected by considering the hardness of the uncoated AISI D2 tool steel. Holding the temperature at 400 °C even for 15 hours had no softening effect on the AISI D2 tool steel. The characteristics of the coatings were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), hardness and scratch tests, and roughness and thickness measurements. The XRD analyses were conducted on a PHILIPS* RV 3710 with Cu K radiation. The incident angle *PHILIPS is a trademark of Philips Electronic Instruments Corp. Mahwah, NJ.
was chosen as 3 deg. The SEM examinations were made using electron dispersive spectroscopy (EDS) on a JEOL† †JEOL is a trademark of Japan Electronic Instruments Corp.,Tokyo.
II. EXPERIMENTAL PROCEDURE In the present study, quenched and tempered AISI D2 tool steel plates were used as the substrate material. The hardness of the substrate was 59 HRC. Binary ZrN and ternary (Zr,Hf)N coatings, containing different amounts of Hf, were deposited on the substrate by arc physical vapor deposition (PVD) after final polishing with a 1-m diamond paste. Arc PVD coating parameters are listed in Table I. ZrN and (Zr,21 pct Hf)N coatings were deposited by using two Zr cath
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