Manufacturing Process Development and Rig Validation of Slurry Environmental Barrier Coatings for SiC Ceramic and SiC Composite Sub-Components

Abstract

The process scale-up of fully oxide-based environmental barrier coatings (EBCs) on sintered SiC and chemical vapor infiltration (CVI) SiC/SiC ceramic matrix composite (CMC) sub-components was investigated using various slurry manufacturing processes (dip, spray, spin–dip). The performance of EBC-coated sub-components (SiC heating element, SiC/SiC ceramic matrix mini-composite, SiC airfoil, SiC/SiC CMC airfoil) was evaluated in steam oxidation and combustion rigs. Steam oxidation was conducted at 1427 °C in 90 vol.% H2O (g) + 10 vol.% O2 (g) with a 1 h hold at 1427 °C per cycle (1 h hot and 20 min cooling). For high-pressure combustion rig testing, the EBC surface temperature ranged between 1354 °C and 1538 °C with the temperature gradient through CMC + EBC ranging between 100 °C and 150 °C. Dip and spin–dip are non-line-of-sight processes, whereas spray is a line-of-sight process. The three processes, collectively, demonstrated the capability to manufacture slurry EBCs on sub-components with various shapes and sizes. There was no discernable disparity in the EBC steam oxidation performance between the coupons and sub-components in this study and coupons in a previous study. The dependence of steam oxidation rates on the substrate chemistry reported previously was confirmed. The steam oxidation rate of EBC-coated sintered SiC, compared with EBC-coated CVI CMC, was ~2 times and ~1.5 times higher after 100 h and 500 h, respectively, due to the boron sintering aid in sintered SiC. An EBC-coated CMC airfoil after 150 15-h-long cycles in a high-pressure combustion rig test showed only limited EBC spallation along the leading edge and more substantial spallation along the trailing edge, demonstrating the feasibility of an oxide-based bond coat to meet the extreme temperature requirements of next-generation EBCs.

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

“…38 Slurry-type coating deposition processes may be an option most readily available for complex geometries desired with additively manufactured SiC-base composites. 39…”

“…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 39 …”

Characterisation techniques for investigating TBC and EBC failure: a review

“…The silicon bond coat improves the adhesion between the coating and substrate , but the silicon imposes a temperature limit to an EBC, given its melting temperature of ~1,416 °C (Desai, 1986;Zhang et al, 2022). Therefore, this has started the development of alternative EBC systems with different bond coats (Anton et al, 2020;Harder, 2020;Lee et al, 2022;Zhang et al, 2022). Comprehensive reviews of other EBC systems and compositions can be found in separate publications Paksoy and Xiao, 2023).…”

“…Identifying and quantifying boron concentrations are important as boron increases the rate of oxidation in EBCs (Lee et al, 2021;Lee et al, 2022). Furthermore, the solubility limit of boron at temperature increases, which could also contribute to accelerated oxidation at higher temperatures (Knauf et al, 2020).…”

β→α Phase Transformation and Properties of Solid-State-Sintered SiC Ceramics with TaC Addition

“…Silicon carbide (SiC) ceramics have excellent properties, i.e., a high strength, high modulus, low thermal expansion, high thermal conductivity, and good corrosion resistance, enabling their widespread use in the nuclear, semiconductor and aerospace industries [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. Densification of SiC ceramics is extremely difficult due to their strong covalent bonds, leading to a low self-diffusion coefficient (~10 −11 cm 2 /s for C and ~10 −13 cm 2 /s for Si) [ 10 ].…”