Strength and Adhesion of Thin Aluminum Oxide Film Deposited on Iron Surface

The strength of deposited film and the adhesion between the film and the substrate were investigated with deposited aluminum oxide film on iron surface by scratching the surface with a diamond cone. Two types of samples were examined, one with oxide film deposited after cleaning the substrate surface by sputter etching, the other with the film deposited without any sputter etching. It was found that a law similar to Meyers’ for indentation hardness holds between the load and scratch width on the sample examined. These results suggest that by analyzing the scratch data the adhesion strength of the film to the substrate can be estimated together with the hardness of the film itself. Analyses by EPMA (electron probe X-ray microanalyzer) and AES (Auger electron spectroscopy) were conducted to correlate the results obtained by the scratch tests and friction experiments, and it was confirmed that (i) adhesion is improved by sputter etching prior to the deposition of the film; (ii) adhesion decreases considerably due to the progress of oxidation in the vicinity of the interface, which depends markedly on the oxygen concentration in the oxide film; and (iii) there is an optimum thickness of the three-component layer (Fe, Al, and O) formed by atomic mixing at the interface for maximizing the adhesion.