Influence of Galvanic Macro-cell Corrosion on the Cavitation Erosion Durability Assessment of Metallic Materials
Akihiro Sakamoto, Hiroshi Funaki, Masanobu Matsumura
Cavitation erosion tests were carried out on five metallic materials which are the standard materials of the International Cavitation Erosion Test Program which is co-ordinated by Dr. J. Steller, Institute of Fluid-Flow Machinery, the Polish Academy of Science, Gdansk, Poland. Three kinds of testing apparatus were used: a vibratory unit, a vibratory unit with a stationary specimen, and a water tunnel. In the two vibratory tests, the ranking order of the materials according to their durability to cavitaition attack showed a complete coincidence with each other. However, the ranking based on the water tunnel test was different from those of the vibratory units. This was because the damage rate of some materials was suddenly accelerated in the middle of water tunnel test. It was revealed that the sudden increase in erosion rate is caused by the electrochemical corrosion which is enhanced by the activation of the damaged surface in atomic level. The corrosion is further promoted when a macrocell of corrosion is formed between the cavitation-damaged area (anode) and the undamaged area (cathode) of the specimen surface.