P. Mishra

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.

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.