Wear and oxidation resistance of combustion CVD grown alumina films

Alumina thin films were synthesized on Si (100) and Ni–20Cr substrates using combustion chemical vapor deposition. Aluminum acetylacetonate (0.005 M) dissolved in ethanol was used as the precursor solution. The films deposited at 900 and 1000 °C are found to be θ-alumina and those deposited at 1100 °C to be α-alumina. The scanning electron micrographs showed the films to be made up of crystallites of two different sizes and shapes. The coefficient of friction, of alumina coated Si samples, measured using a tribometer showed high value (~ 0.7) at initial passes and subsequently saturated to low value (~ 0.5) at higher sliding distances. It was observed that the tribological properties, of the films, are not affected significantly by the crystal structure and crystallite size. Oxidation resistance of alumina-coated Ni–20Cr specimens were studied using a thermo-gravimetric analyzer by exposing them to isothermal heating at 1000 °C in 20% O2–Ar gas mixture. The results indicated that the coated specimens are 18 times more oxidation resistant, at initial stages, compared to uncoated specimens. The resistance slowly dropped to six times, where it reached a saturation value.