Sermatech International Inc.

Stephen G Sitko

Purusottam Sahoo

A strain tolerant ceramic coating, preferably for use as an abrasive coating on a substrate is provided. The coating is prepared from a yttria and zirconia powder having an average particle size less than 40 microns. The coating is formed by depositing the powder on the substrate by a plasma spray process. The as-applied coating contains essentially no macrocracks, but a post-stressed coating contains a random distribution, population, and orientation of microcracks and macrocracks.

Strain tolerant ceramic coating

Known thermal spray apparatus are modified to achieve thermal spray coatings of increased hardness. Thermal spray apparatus operate to develop a plasma stream for introduction to a nozzle, for eventual application to the surface of a substrate. Upon entering the nozzle, the plasma stream is passed through a plasma cooling zone defined by a plasma cooling passageway, to a plasma accelerating zone defined by a narrowed passageway that expands into a plasma/particle confining zone for the discharge of material from the apparatus. The narrowed passageway of the apparatus is cooled, and the powder material to be applied by the apparatus is introduced into the plasma stream along the cooled, narrowed passageway. To apply thermal spray coatings of increased hardness to a substrate, the ratio of the length of the plasma/particle confining zone relative to the diameter of the plasma/particle confining zone (the 'L/D' ratio) is increased from the more conventional value of about 5:1, preferably to a ratio in a range of from 7:1 to 16.5:1, for use with coating materials including WC--Co, Cr.sub.3 C.sub.2 --NiCr and Cr.sub.3 C.sub.2. Ratios of from 10:1 to 13:1 have been found to achieve a particularly desirable result. Also the method and the coatings obtained.

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Telford, PA, United States of America

Stephen G Sitko