Mullite–gadolinium silicate environmental barrier coatings for melt infiltrated SiC/SiC composites

• Published in: Surface & coatings technology 2011-03, Vol.205 (12), p.3578-3581
• Main Authors: Ramasamy, Sivakumar, Tewari, Surendra N., Lee, Kang N., Bhatt, Ramakrishna T., Fox, Dennis S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Barriers; Coatings; Cracks; Cross-disciplinary physics: materials science; rheology; Damage; Electron microscopy; Environmental barrier coatings; Exact sciences and technology; Fiber reinforced composites; Fibre reinforced metals; Materials science; Melts; Metals. Metallurgy; Mullite; Oxidation; Physics; Powder metallurgy. Composite materials; Production techniques; Silicates; Silicon carbide; Sintered metals and alloys. Pseudo alloys. Cermets; Sintering; Surface treatment; Surface treatments; Thermal cycling
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2010.12.031

Slurry based mullite/gadolinium silicate (Gd2SiO5) environmental barrier coatings (EBCs) were developed for melt infiltrated (MI) SiC/SiC composites. The coating chemically adhered well on the substrates. Thermal cycling of uncoated MI-SiC/SiC composites conducted between 1350°C and 90°C (one hour hot and 15min cold) in a 96.5% H2O–3.5% O2 environment caused severe oxidation damage after 100 cycles resulting in the formation of dense silica layer of about 25μm maximum thickness. Mullite/Gd2SiO5 EBCs provided excellent protection to MI-SiC/SiC against moisture damage with significantly less oxidation of the substrate; only about a 2μm thick oxide layer formed even after 400 similar thermal cycles. The hair-line cracks formed at the coating/substrate interface after 400 cycles causing partial coating de-lamination. ► Mullite/Gd2SiO5 EBC chemically adhered well on MI-SiC/SiC composites after sintering. ► Severe oxidation damage occurred for un-coated MI-SiC/SiC after 100 thermal cycles. ► EBC protected MI-SiC/SiC had minimal oxidation damage even after 400 thermal cycles.