Crystallization behavior of arc-deposited ceramic barrier coatings

Al2O3 and Er2O3 were deposited by plasma-assisted physical vapor deposition using a filtered vacuum arc device. Varying the deposition conditions with respect to the substrate temperature and bias voltage, the crystallization behavior of these films was investigated by X-ray diffraction. In the case of alumina, when a bias voltage of −200 V is applied, crystallization of metastable crystal phases starts around 500 °C; the growth of the thermodynamically stable α-phase starts above 600 °C. This has to be compared with the thermodynamic phase transformation temperature of 1100 °C. For erbia, crystallization of the cubic crystal phase occurs at room temperature, when a bias voltage of −100 V is applied. Without exceeding the upper service limit, structural low activation materials can therefore be coated with stable ceramic barrier coatings. Deuterium permeation experiments performed with these types of coatings yield a permeation reduction factor of 40 in the case of alumina and 200 for erbia, respectively.