Strict tolerances on the dimensions of O-ring sealing surfaces often cause the replacement of components used in seawater systems which have slight corrosion damage. The application of thermal sprayed coatings offers a potentially effective repair method for corrosion damaged components.

Static seawater immersion tests were conducted to evaluate the performance of four thermal spray ceramics: two alumina based, one chromia based and one zirconia based. These ceramic coatings were applied to alloy NO6625, alloy NO4400 and alloy C71500 with and without a sprayed metal undercoat. Specimens were exposed for up to 20 months, and provided boldly exposed surfaces as well as O-ring sealing surfaces.

Results showed the thermal sprayed ceramics to perform well in seawater, with the exception of the chromia based coating. The zirconia and the alumina based ceramic coatings all displayed performance superior to the substrate alloys under O-rings. The ceramics were found to be resistant to corrosion both in crevices and on boldly exposed surfaces, while all three substrate materials were found to be susceptible to crevice corrosion under O-rings. The thermal sprayed metal undercoats were also found to be susceptible to attack under the conditions tested.

Alloy NO6625 was applied as a thermal sprayed coating to alloy NO4400. O-ring sealing surfaces coated with alloy NO6625 had better crevice corrosion resistance than uncoated alloy NO4400.

Subject
Materials, Substrates, Metal surfaces, Chromia, Seawater, Substrate surfaces, Corrosion attacks, Crevice corrosion, Metals, Specimen preparation, Ceramics, Ceramic coatings, Alloys
© 1990 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1990
Association for Materials Protection and Performance (AMPP)
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