Abstract
In order to improve the ability of ceramics to withstand cavitation attack, two schemes were tried. One was to strengthen the bulk of ceramics through preparing powder of very fine aluminum oxide particles with uniform diameter, which was casted tightly by applying centrifugal force on it before sintering. The alumina ceramics manufactured by this method had a fracture toughness twice that of current alumina ceramics, resulting in a cavitation erosion rate as low as one sixth of that of current alumina ceramics. The other was the dynamic ion mixing method where a very hard and adherent layer of titanium nitride was built on the surface of a base metal of austenitic stainless steel (SUS 304) by implanting nitrogen ion in it and depositing titanium on it simultaneously. The titanium nitride layer of 10μm thickness on the metal had a Vickers hardness of 3500, and prolonged the incubation period of the composite material by fifty times that of base metal. It was discussed that manufacturing cost, characteristics of the materials as well as the level of size precision should be taken into account when these newly developed materials are put in the material selection for hydraulic machine parts.
