Improved Compatibility of A New Ni Base Alloy with Supercritical Water Applications: Beneficial Effects of Ta Addition on Corrosion Resistance and Aging Susceptibility

摘要

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 deg C to 650 deg 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 deg C - 650 deg 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.