Abstract
Appropriate conditions for depositing hard Cr2O3 coatings by reactive sputtering techniques have yet to be defined. To fill this gap, the effect of principal deposition parameters, including deposition pressure, temperature, Cr-target voltage, and Ar/O2 ratio, on both the structure and mechanical properties of chromium oxide coatings was investigated. A relationship between processing, structure, and the mechanical properties of chromium oxide coatings was established. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the morphology, structure, and chemical compositions of the coatings that were prepared. An optical profilometer was employed to measure both the roughness and thickness of the coatings. The hardness and Young’s modulus of the coatings both as-deposited and after annealing conditions were measured by nanoindentation. The results showed that depositing hard Cr2O3 coatings is a highly critical task, requiring special deposition conditions. Cr2O3 coatings with a high hardness of approximately 25 GPa could be achieved at room temperature, at a low pressure of 1.6 × 10−1 Pa, where Cr-target voltage and oxygen content were 260 V and between 15–25 vol % of total gas, respectively. A dense stoichiometric Cr2O3 structure was found to be responsible for the high chromium oxide coating hardness observed.
Highlights
Bulk Cr2 O3 is one of the hardest oxides, with a hardness of 29.5 GPa [1,2,3,4], and can be deposited as a protective coating for many purposes, due to its high wear resistance, low coefficient of friction, and excellent corrosion resistance [5,6,7]
Chromium oxide coatings deposited by sputtering methods can show weak mechanical properties if appropriate deposition parameters are not selected during the deposition process
The various forms of chromium oxides, with different microstructures and chemical compositions, could be the main reason for the wide range of mechanical properties in chromium oxide coatings deposited under nonequilibrium sputtering conditions at low temperatures and pressure
Summary
Bulk Cr2 O3 is one of the hardest oxides, with a hardness of 29.5 GPa [1,2,3,4], and can be deposited as a protective coating for many purposes, due to its high wear resistance, low coefficient of friction, and excellent corrosion resistance [5,6,7]. Many methods, including plasma-spray [8,9,10], sputtering [11,12], chemical vapor deposition (CVD) [13], and pulsed laser deposition [14], have been used to produce Cr2 O3 coatings. The various forms of chromium oxides, with different microstructures and chemical compositions, could be the main reason for the wide range of mechanical properties in chromium oxide coatings deposited under nonequilibrium sputtering conditions at low temperatures and pressure. In this context, Hones et al [3] investigated the effect of deposition temperature and oxygen partial pressure
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