Abstract
Water vapor is a constituent in many environments of technical significance, especially those associated with combustion, and the switch to hydrogen-firing will increase the concentration of water vapor in the exhaust. A negative influence of water vapor on high temperature oxidation has long been recognized for both metallic and ceramic components by comparing laboratory exposures with and without water vapor. However, the effect of water vapor concentration has not been studied as frequently. Several data sets will be reviewed including alloys for thin-walled gas turbine recuperators and the performance of uncoated superalloys and alumina-forming alloys and coatings including the performance of thermal barrier coatings in furnace cycle testing. Chromia-forming alloys are more severely degraded by water vapor in exhaust due to the volatilization of CrO2(OH)2 and this reaction may be faster with higher water vapor contents. Alumina-forming alloys and coatings exhibit some degradation with the addition of water vapor but no impact of increasing the water vapor content has been observed. For silica-forming ceramics, water vapor has an extreme impact on the growth rate and the performance of environmental barrier coatings can be evaluated based on the underlying silica growth rate.