Metal organic chemical vapor deposition of Al2O3 and Cr2O3 on nickel as oxidation barriers

Aluminum oxide and chromium oxide were deposited onto untreated and pre-oxidized Ni coupons by metal–organic chemical vapor deposition. Oxidizing the surface prior to the deposition of the ceramic coating has been studied to determine the effect of the intermediate oxide layer. The metal oxide coatings were obtained from their respective metal acetylacetonate precursors. The pyrolysis reactions were carried out under atmospheric conditions. Amorphous Al2O3 was obtained at a deposition temperature of 500 °C and crystalline Cr2O3 with the corundum structure was obtained at 450 °C. The effectiveness of the metal oxide coatings as barriers were evaluated by oxidation experiments at 800 °C for 120 h. Samples coated with Al2O3 exhibited a significant decrease in oxidation rate. However, Cr2O3 coated on both untreated and pre-oxidized samples were not effective barrier coatings. Samples involving Cr2O3 deposited on untreated Ni showed an increase in oxidation rate whereas samples with Cr2O3 on heat-treated Ni showed a similar oxidation rate as uncoated Ni. The microstructures were investigated with scanning electron microscopy. Composition and crystalline structures were determined with X-ray diffraction and elemental analysis.