R. K. Choudhary

Deposition of rock salt AlN coatings by magnetron sputtering

Abstract Cubic aluminium nitride (AlN) coatings were successfully deposited on stainless steel 304L substrates by balanced magnetron sputtering. Grazing incidence X-ray diffraction measurement confirmed the formation of rock salt cubic AlN having a preferred orientation along (111) plane. Scanning electron microscopy revealed nodular microstructure of the coating. Thermal diffusivity of AlN coated sample was found to be significantly higher than that of the uncoated sample. Microscratch adhesion test showed no adhesive failure below 20 N loads.

Optical properties of cubic AlN films grown by sputtering

Cubic aluminium nitride (AlN) films were deposited on stainless steel substrate by reactive balanced magnetron sputtering. The film was studied for its optical properties using spectroscopic ellipsometry technique. A maximum band gap of 5·52±0·26 eV was obtained for the deposited film. The maximum value of refractive index measured in the wavelength range of 300–1100 nm was 1·9–2·15. Grazing incidence X-ray diffraction of the film showed formation of (200) oriented cubic AlN.

Stirring effects on aluminium coatings electrodeposited in ionic liquids

Abstract Aluminium coatings were electrodeposited on Fe9Cr1Mo steel from AlCl3–1-ethyl-3-methyl imidazolium chloride ionic liquid at room temperature and the effect of solution stirring on deposition rate, preferred crystal orientation, surface morphology and roughness have been investigated. Aluminium coating could not be obtained in the unstirred solution for a deposition current density of 20 mA cm−2 or higher. However, vigorous stirring of the bath enabled the deposition at a current density of 20 mA cm−2 or higher, along with a significant increase in coating thickness. On the other hand, roughness of the coating increased at higher stirring speeds. X-ray diffraction measurement showed 26% increase in normalised intensity of (111) reflection on increasing the stirring speed up to 800 rev min−1, whereas the intensity of (200) reflection was found to be decreased by 37%. Scanning electron microscopy and energy dispersive X-ray analysis of the anodised aluminium showed formation of less porous aluminium oxide film.

Pulse DC electrodeposition of Zn–Ni–Co coatings

Anomalous co-deposition of Zn–Ni–Co ternary alloy on carbon steel and copper substrates was attempted using pulse direct current electrodeposition technique. The obtained coatings were characterised for their crystal structure, chemical composition and surface morphology by X-ray diffractometry, energy dispersive X-ray spectroscopy and scanning electron microscopy, respectively. X-ray diffraction measurement showed peaks for Zn, Ni and Co. The concentration of Ni and Co in the ternary alloy increased with decrease in pulse frequency as confirmed by energy dispersive X-ray measurement. Scanning electron microscopy revealed uniform morphology of the coating surface with an average grain size of 1 µm. Potentiodynamic polarisation and electrochemical impedance spectroscopy tests conducted in 3% NaCl solution confirmed improved corrosion behaviour of the coatings deposited at lower current pulse frequencies.

Substrate and current density effects on electrodeposited aluminium coatings

Abstract Coatings of aluminium were electrodeposited on copper and mild steel substrates in a room temperature ionic liquid (RTIL) using [EMIm]Cl (95%) and AlCl3 (98%) in a glove box having a controlled atmosphere. Formation and purity of aluminium were confirmed by X-ray diffraction, X-ray fluorescence and energy dispersive spectroscopy measurements. Microcrystalline grain morphology of deposited Al was observed in scanning electron microscopy. The present study showed that Al coating electrodeposited in an RTIL exhibited similar morphology on copper and mild steel substrates, and cathode current efficiency depended on purity of the electrolyte and also on the deposition current density. There were indications for build-up of tensile stress in the coating even at low deposition current density.

Structural and optical properties of anodic orthorhombic zirconia films

ABSTRACT Twenty to eighty nanometre thick zirconia (ZrO2) films were formed by anodisation of zirconium metal in 10% oxalic acid in the potential range of 10–30 V. Grazing-incidence X-ray diffraction measurement revealed the formation of orthorhombic ZrO2. X-ray photo electron spectroscopy confirmed the formation of nearly stoichiometric ZrO2 at 20 V. Ellipsometric measurement across the visible spectral band derived the value of refractive index of ZrO2 films in the range of 2.02–2.2.

Mechanical and tribological properties of rhombohedral diamond-rich coatings grown on stainless steel by hot filament CVD

In this study, rhombohedral diamond-rich coatings were grown directly on stainless steel (SS) substrate and also on sputter deposited titanium nitride interlayer, by hot filament chemical vapour deposition technique. Grazing incidence X-ray diffraction measurement of the coatings confirmed the formation of polycrystalline rhombohedral phases of diamond. Field emission scanning electron microscopy revealed a jelly type morphology of the coatings. The coating deposited with titanium nitride interlayer showed improved resistance against scratch indentation, lower wear rate and had lower value of coefficient of friction in comparison to the coating deposited directly on SS.

Effect of substrate temperature and nitrogen concentration during sputtering on corrosion behaviour of AlN coatings

Aluminium nitride coatings were formed on stainless steel substrate by DC-reactive balanced magnetron sputtering at various nitrogen concentrations in the sputtering gas mixture, and different substrate temperatures. The electrochemical corrosion behaviour of the coatings obtained was studied in 0.5 M H2SO4. Continuous improvement in corrosion resistance of the coatings was observed with increasing coating deposition temperature up to 500 °C. The corrosion potential shifted from −0.66 VSCE at 100 °C to −0.33 VSCE at 500 °C. Accordingly, the corrosion current density decreased significantly with increase in the deposition temperature. However, no major difference in corrosion behaviour could be noticed for the coatings formed at various nitrogen concentrations.