Steam oxidation and microstructural evolution of rare earth silicate environmental barrier coatings

Abstract

A primary failure mode for environmental barrier coatings (EBCs) on SiC ceramic matrix composites (CMCs) is the oxidation of the intermediate Si‐bond coating, where the formation of SiO2 at the bond coating–EBC interface results in debonding and spallation. This work compares the microstructure evolution and steam oxidation kinetics of the Si‐bond coating beneath yttrium/ytterbium disilicate ((Y/Yb)DS) and ytterbium disilicate/monosilicate (YbDS/YbMS) EBCs to better understand the impact of EBC composition on oxidation kinetics. After 500 1‐h cycles at 1350°C, (Y/Yb)DS displayed a decreasing concentration of the monosilicate minor phase and increasing concentration of porosity as furnace cycling time increased, whereas the YbDS/YbMS EBC displayed negligible microstructural evolution. For both EBC systems, thermally grown oxide growth rates in steam were found to increase by approximately an order magnitude compared to dry air oxidation. The (Y/Yb)DS EBC displayed a reduced steam oxidation rate compared to YbDS/YbMS.

Oxidation performance and limitations of additively manufactured SiC/Si─O─C composites at elevated temperatures

“…Further, it is known that SiO 2 undergoes a phase transformation upon cooling around 250 • C which results in cracking. [29][30][31][32] Fast removal of the C-rich phase encouraged additional cracking of the residual SiO 2 phase to create more oxidant pathways for subsequent exposures.…”

“…Complex ceramics with low oxidant diffusivities remains an active area of research, yet many environmental barrier coating candidates are currently available. 10,32,37 Standard deposition methods for high-temperature ceramic coatings focus on plasma spray processes that are primarily line-of-sight. 38 Slurry-type coating deposition processes may be an option most readily available for complex geometries desired with additively manufactured SiC-base composites.…”

“…The decreased C content agrees with qualitative image analysis of the C‐rich matrix phase, previously discussed, where a lower C content would result in decreased concentration of porosity formation, as the porosity uptake was linked to CO 2 formation. Further, it is known that SiO 2 undergoes a phase transformation upon cooling around 250°C which results in cracking 29–32 . Fast removal of the C‐rich phase encouraged additional cracking of the residual SiO 2 phase to create more oxidant pathways for subsequent exposures.…”

“…It is clear that protective coatings should be applied for immediate improvements in performance. Complex ceramics with low oxidant diffusivities remains an active area of research, yet many environmental barrier coating candidates are currently available 10,32,37 . Standard deposition methods for high‐temperature ceramic coatings focus on plasma spray processes that are primarily line‐of‐sight 38 .…”

Effects of yttrium doping on high-temperature oxidation, friction, and wear properties of CrAlN films

“…The remarkable physicochemical properties of rare earth elements have made them 'industrial gold.' Their unique physical and chemical properties have widespread applications in various fields, such as military, electronics, metallurgy, optics, agriculture, chemicals, and medicine [1][2][3][4][5]. Recent research has shown that surface treatment can introduce the right amount of reactive yttrium (Y) content into nitride hard films, thereby improving their hardness, adsorption capacity, and resistance to high-temperature oxidation.…”