Transport properties and microstructure changes of alumina coatings characterized by emanation thermal analysis

Emanation thermal analysis was used to characterize the thermal behaviour of alumina coatings as deposited on EUROFER 97 steel surface by filtered vacuum arc technique. Temperature ranges of the healing of cracks and structure irregularities observed by SEM were determined from the ETA results. Transport properties of the alumina coatings were assessed from the ETA results by the evaluation of radon diffusion parameters in the temperature range from 50 to 300 degrees C. Healing microstructure irregularities of the alumina coatings can be expected in the range 300-700 degrees C as indicated by the decrease of the radon release rate. From the ETA results it followed that the onset of healing the cracks observed by the SEM on the surface of one alumina coating sample can be expected at 430 degrees C.