Microstructure and mechanical properties of chromium oxide coatings
- PDF / 818,105 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 83 Downloads / 253 Views
Kewei Gaoa) Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China
Alex A. Volinsky Department of Mechanical Engineering, University of South Florida, Tampa, Florida 33620 (Received 2 August 2007; accepted 12 September 2007)
Chromium oxide coatings were deposited on low-carbon steel by radiofrequency reactive magnetron sputtering at different oxygen flux values. X-ray diffraction, x-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy were used to investigate the microstructure of chromium oxide coatings. Varying oxygen flux changed the coating microstructure; as with increasing oxygen flux the chromium oxide coating undergoes amorphous-to-crystalline transformation. The coating developed strong (300) texture at higher oxygen flux. Hardness, elastic modulus, wear resistance, and adhesion were investigated by nanoindentation and pin-on-disk tests. With changes in the coating microstructure as a function of increased oxygen flux, hardness, elastic modulus, and wear resistance were improved, but its adhesion was weakened. I. INTRODUCTION
Chromium oxide is the hardest oxide that also exhibits low friction coefficient, high wear and corrosion resistance, and good optical and adiabatic characteristics. These properties allow for it to be used as a protective coating in tribological and microelectronic applications and as an adiabatic material in aeronautic and space fields.1–4 Many techniques have been developed to deposit chromium oxide coatings, including thermal plasma spraying, chemical vapor deposition, and ion implantation. Among them, reactive radiofrequency (rf) magnetron sputtering is most suitable for industrial production and makes it possible to achieve high-quality Cr2O3 stoichiometric coating with nearly 30 GPa hardness combined with good scratch resistance.5 The advantage of reactive magnetron sputtering for this purpose is mainly due to the high deposition rate achieved by sputtering from a metal target versus an oxide target.6 Mechanical and adhesion properties of coatings are affected by its microstructure. Sputtered coating microstructure and physical characteristics depend on the
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0445 J. Mater. Res., Vol. 22, No. 12, Dec 2007
http://journals.cambridge.org
Downloaded: 23 Jan 2015
deposition parameters,7–9 which in reactive sputter deposition play an important role to achieve a strictly stoichiometric ratio of Cr2O3; therefore, oxygen flux becomes especially important for oxidation. Different stoichiometric ratios exhibit vastly different mechanical properties in chromium oxide coatings.10–12 High adhesion is known to ensure the prolonged lifetime of the coating and to promote good wear resistance.7 Good coating adhesion is required for wear- and corrosionresistance applications. Premature failures can occur for many reasons, including coating delamination, cracking, and plastic deformation. In addition to
Data Loading...
