Deposition and characterization of SixC1 − x/Al2O3 coatings by magnetron sputtering for nuclear fusion applications

Al2O3 coatings were fabricated on CLAM steel substrates at 300 °C by RF magnetron sputtering, and SixC1 − x coatings with different Si concentrations were then fabricated on the Al2O3 coatings by pulse magnetron sputtering. The coating composition, topography, structure and mechanical properties were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), X-ray diffractometry (XRD), Raman spectroscopy, nano-indentation techniques and scratch tests. The results show that SixC1 − x coatings had Si contents in the range 39–62 at.%. Al2O3 coatings exhibited an island growth mode, while SixC1 − x coatings showed a step flow growth mode. Compact and crack-free SixC1 − x/Al2O3 Coatings were prepared. α-Al2O3, α-Cr2O3 and spinel Fe2CrO4 were all detected in the Al2O3 coating by Raman spectroscopy. The hardness and elastic modulus of the Al2O3 coating were 15.5 ± 1.0 and 194.8 ± 7.2 Gpa, respectively. The hardness and elastic modulus of SixC1 − x layer were 28.6 ± 0.8 Gpa and 219.2 ± 2.6 Gpa, respectively, for Si content of ≈ 49 at.%. The adhesion of C-rich and stoichiometric SixC1 − x/Al2O3 coatings were superior to those of Si-rich coatings.

Research highlights
► Alpha alumina coatings were deposited at 300 °C by pluse magnetron sputtering.
► Compact and strong adhesion SixC1 − x/Al2O3 coatings were prepared.
► The surfaces of SixC1 − x/Al2O3 coatings are smoother than that of Al2O3 coating.