Synthesis and Characterization of Hard Cr2O3 and Superhard Cr-Zr-O PVD Coatings

Abstract

Reactive radio-frequency magnetron sputter technique (RF-MS) was used to deposit Cr-O and Cr-Zr-O coatings on silicon, SS316L, WC-Co, and HSS M42 substrates. The effects of deposition temperature, chemical composition, and subsequent heat treatment on microstructural, thermal stability, and mechanical properties of both Cr-O and Cr-Zr-O coatings were investigated. The deposited coatings were characterized using scanning electron microscopy, Xray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, Energy dispersive spectroscopy, nanoindentation, Rockwell “C” indentation, optical profilometer, reciprocating wear testing, electrochemical testing, and inductively coupled plasma analysis. The results showed that appropriate deposition conditions were required in order to obtain hard Cr2O3 coating. A Cr2O3/Cr duplex interlayer was found to be suitable for nucleation of diamond coatings on WC-Co substrates as it restricted graphite formation before diamond nucleation, thus, continuous diamond coatings with good adhesion were successfully deposited on Cr2O3/Cr interlayered WC-Co substrates. Furthermore, hard Cr2O3 coatings were shown to be a potential candidate to improve the mechanical properties and to reduce the toxic ion release rate of orthopedic implants. The coated SS316L substrates illustrated better wear and corrosion resistance and lower friction coefficient compared to bare 316L substrates under a reciprocating sliding condition in saline solution. Furthermore, many fewer Cr ions were released from coated SS316L substrates after immersion tests. Adding zirconium to Cr2O3 coating shifted the onset of crystallization for the Cr2O3 coating to higher temperatures and superhard Cr-Zr-O coatings with a hardness value over 40 GPa could be obtained at a zirconium concentration of around 9.5 at. % and a substrate temperature of 300°C. The obtained superhardness could be attributed to the formation of a nanocomposite structure.