Nickel base corrosion resistant alloys are thought to be strong candidates as a structural material for chemical processes using supercritical water (SCW). Long-term plant operation at expected temperature range of SCW processes, 400 °C to 650 °C, however, is very likely to cause phase transformation and resultant degradation in properties, because nickel base corrosion resistant alloys are usually applied as solution heat treated condition and have relatively poor phase stability.

In this paper, an exploratory study has been done to find a new nickel base alloy, which has improved phase stability and low susceptibility to aging degradation. Hardness, impact toughness, and corrosion resistance in acidic supercritical water have been evaluated on Ni-Cr experimental alloys with small quantity of various third elements before and after aging heat treatments at 400 °C – 650 °C for up to 3000 hours. It was found that tantalum addition to Ni-Cr alloy remarkably mitigates aging degradation of the alloy both in mechanical properties and corrosion resistance.

Subject
Stability, Supercritical water, Tantalum, Corrosion resistant alloys, Nickel based alloys, Molybdenum alloys, Chromium, Copper alloys, Commercial alloys, Corrosion resistance, Nickel, Aluminum alloys, Aging
Keywords:
supercritical water, corrosion, phase stability, nickel base alloy, tantalum, toughness, Charpy impact value, aging degradation
© 2004 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).
2004
Association for Materials Protection and Performance (AMPP)
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