Erosion behaviour of ceramic bulk and coating materials caused by water droplet impingement

Turbine blades in the low-steam environment of energy generation systems suffer severe erosion due to the impingement of water droplets. Erosion resistance of metallic substrates to droplet impingement could possibly be improved with ceramic coating. However, the erosion resistance of ceramic material has not been sufficiently evaluated with respect to selection and maintenance of component materials in power plant systems. A water-jet apparatus, for which impingement velocity and number of water droplets have been well characterized, was used in this study. Erosion tests were conducted on various ceramic bulk and coating materials and on the metallic substrates to investigate erosion behaviour and resistance. Erosion behaviour was characterized by the incubation period and the subsequent damage depth rate. Some ceramic bulk materials had short incubation periods and significant damage depth rates. Zirconia normally had the longest incubation periods and the lowest damage depths. The erosion rate was calculated from the relationship between logarithms of damage depth and impact velocity. The incubation period was also correlated with the logarithm of impact velocity. Both velocity constants in erosion damage and incubation periods of these ceramic materials were strongly correlated with fracture toughness, but not with hardness of the materials. Damage depth rates calculated from the relationship with impact velocity and fracture toughness were comparable to experimentally measured damage depth rates for various ceramic materials.