Ceramics-Silikáty 52 (2) 85-89 (2008)

USE OF EMANATION THERMAL ANALYSIS IN THE MICROSTRUCTURE DIAGNOSTICS OF ALUMINA COATINGS

V. Balek, M. Beneš, J. Šubrt

Emanation thermal analysis (ETA), based on the radon release measurements, was used characterize the microstructure development of alumina coatings on heating. The alumina coatings were deposited on EUROFER' 97 steel surface by using the filtered vacuum arc technique. Healing of microstructure irregularities that served as radon diffusion paths in the alumina coatings was characterized as a decrease of the radon release rate in the range 300-700°C. The healing of surface micro-cracks observed by SEM micrographs on the alumina coating sample was characterized as the break on the temperature dependence of radon release rate in the temperature range 430 -660°C. From the ETA results it followed that healing of the microstructure irregularities in the range of 300-700°C was depending on the conditions used for the alumina coatings preparation. A higher intensity of this process can be expected with the alumina coating of 4 µm thickness in comparison with the alumina coating of 0.5 µm thickness.

Keywords: Alumina coatings, Emanation thermal analysis, SEM, Microstructure irregularities, Cracks healing