Role of Al oxide PVD coatings in the protection against metal dusting

The presence of some surface oxides in materials exposed to metal dusting has been proven to be an effective method to prevent this type of corrosion due to the very low diffusivity of carbon in oxides. However, the surface oxide films have to be dense and adhere well to the component to be protected. Reactive magnetron sputtering (RMS) is a promising method to produce these types of oxide layers due to its flexibility in terms of process parameters and resulting structures. In the present work, Al oxide/Al layers have been deposited by RMS on HK40 substrates under various conditions in order to develop the most adequate structure for protection against metal dusting. Some coated substrates were subjected to metal dusting conditions in a thermobalance. The microstructure of the coatings before and after metal dusting was characterized by scanning electron microscopy, atomic force microscopy and x-ray diffraction. Bias voltage was found to be the most important deposition variable for the development of dense adherent films. The coatings showed a protective behavior during the carburization experiments, however more work is needed to optimize the structure of the coatings for more effective protection.