Structure and properties of Cr2O3 coatings deposited using DCMS, PDCMS, and DOMS

• Improved crystallinity of the Cr2O3 coatings deposited by DOMS and PDCMS
• Higher substrate saturation temperature during DOMS Cr2O3 coating deposition
• Ion and electron bombardment oscillation during DOMS depositions
• High hardness and excellent wear resistance of the DOMS Cr2O3 coatings

The crystallinity of oxide phases strongly affects the properties of oxide coatings. In general, a well-crystallized oxide coating is desired because it usually results in improved mechanical and chemical properties. This paper presents a comparative study of the chromium oxide (Cr2O3) coatings deposited by deep oscillation magnetron sputtering (DOMS), mid-frequency pulsed dc magnetron sputtering (PDCMS) and continuous dc magnetron sputtering (DCMS) without applying external substrate heating. The DOMS-Cr2O3 coating deposition showed a peak substrate current density of 65 mA cm− 2 and a substrate saturation temperature of 250 °C, while the DCMS process exhibited a mean substrate current density of 1.29 mA cm− 2 and the lowest substrate saturation temperature of 212 °C. The sputtering techniques strongly affected the crystallinity of the Cr2O3 coatings. The DCMS-Cr2O3 coating exhibited an amorphous like structure. The PDCMS-Cr2O3 coating contained a mixture of amorphous and crystalline α-Cr2O3 phases. In contrast, the DOMS-Cr2O3 coating showed a strong crystallinity with a (110) preferential orientation. The improved crystallinity of the DOMS-Cr2O3 coating is attributed to the enhanced ion flux bombardment and a higher substrate saturation temperature, which is correlated to the energetic electron bombardment observed from the oscillatory substrate current. With the improved crystallinity, the DOMS-Cr2O3 coatings exhibited significantly improved mechanical properties (a hardness of 35 GPa) and wear resistance (a dry coefficient of friction of 0.37 and a wear rate of 5.7 × 10− 7 mm3 N− 1 m− 1) as compared to the coatings deposited using DCMS and PDCMS.