Chemical, morphological and nano-mechanical characterizations of Al2O3 thin films deposited by metal organic chemical vapour deposition on AISI 304 stainless steel

Amorphous alumina coatings of different thickness have been deposited on AISI 304 stainless steel substrates by MOCVD in a hot wall reactor at 380 °C under O2/H2O atmosphere. The used aluminium precursor was the high volatile and easy to prepare dimethyl-aluminum-isopropoxide. Selected films were annealed in N2 and O2 atmosphere at 500 and 700 °C to evaluate the effects of the thermal treatments on the morphology and on the nano-mechanical properties of the coatings. X-ray diffraction and Rutherford backscattering spectroscopy measurements indicated that both the as grown and annealed films were amorphous and very pure with the correct Al2O3 stoichiometry. The surface morphology, investigated by atomic force microscopy, was free of cracks with a roughness of the films that increases with deposition time and with annealing in oxygen atmosphere. The hardness and the elastic modulus of the films and of the AISI 304 stainless steel substrate were measured by load-depth nano-indentation tests. The results highlighted a significant increase in the Berkovich hardness of the coated samples compared to that of the bulk AISI 304 stainless steel.