Stability and CMAS Resistance of Ytterbium‐Silicate/Hafnate EBCs/TBC for SiC Composites

Multilayer ytterbium-hafnate/silicate coatings deposited by directed vapor deposition and designed to protect SiC-based ceramic matrix composites were assessed to determine their thermochemical stability and resistance to attack by molten silicate deposits (CMAS). The study revealed that reactions occurring at the interface between Yb2Si2O7 and Yb4Hf3O12 layers promote coating delamination following isothermal annealing for 100 h/1500°C while coating architectures involving Yb2SiO5 in contact with Yb4Hf3O12 do not experience similar degradation. The outer Yb4Hf3O12 layers, segmented for compliance, were only moderately effective in mitigating CMAS infiltration at 1300°C and 1500°C. The results indicate that the reaction between the melt and coating forms large volumes of a silicate garnet phase at 1300°C, or a cuspidine-type aluminosilicate at 1500°C, in addition to the apatite and reprecipitated fluorite phases observed in related systems.

[1]  C. Levi,et al.  Calcium–Magnesium Alumino‐Silicate Interaction with Yttrium Monosilicate Environmental Barrier Coatings , 2010 .

[2]  K. Fukuda,et al.  Anisotropic thermal expansion in yttrium silicate , 2003 .

[3]  R. Roy,et al.  A New Family of Rare Earth Compounds , 1962 .

[4]  Kang N. Lee.  Current status of environmental barrier coatings for Si-Based ceramics , 2000 .

[5]  A. Kawahara,et al.  The refinement of the crystal structure of cuspidine , 1977 .

[6]  J. Yang,et al.  Thermochemical Interaction of Thermal Barrier Coatings with Molten CaO–MgO–Al2O3–SiO2 (CMAS) Deposits , 2006 .

[7]  I. Spitsberg,et al.  Thermal and Environmental Barrier Coatings for SiC/SiC CMCs in Aircraft Engine Applications* , 2005 .

[8]  Narottam P. Bansal,et al.  Upper Temperature Limit of Environmental Barrier Coatings Based on Mullite and BSAS , 2003 .

[9]  Julie M. Drexler,et al.  Composition effects of thermal barrier coating ceramics on their interaction with molten Ca–Mg–Al–silicate (CMAS) glass , 2012 .

[10]  Carlos G. Levi,et al.  CMAS degradation of environmental barrier coatings , 2007 .

[11]  F. Aldinger,et al.  Phase relationships in the systems RE2O3-Al2O3-SiO2 (RE = rare earth element, Y, and Sc) , 1998 .

[12]  D. Dingwell,et al.  Viscosity of magmatic liquids: A model , 2008 .

[13]  Carlos G. Levi,et al.  Environmental degradation of thermal-barrier coatings by molten deposits , 2012 .

[14]  H. Seifert,et al.  Phase equilibria and thermodynamics in the Y2O3-Al2O3-SO2- system , 2001 .

[15]  P. Mechnich,et al.  Effect of CMAS Deposits on MOCVD Coatings in the System Y2O3–ZrO2: Phase Relationships , 2013 .

[16]  A. Evans,et al.  Mechanisms of cracking and delamination within thick thermal barrier systems in aero-engines subject to calcium-magnesium-alumino-silicate (CMAS) penetration , 2008 .

[17]  J. Yang,et al.  Infiltration‐Inhibiting Reaction of Gadolinium Zirconate Thermal Barrier Coatings with CMAS Melts , 2008 .

[18]  H. Seifert,et al.  Phase equilibria and crystal chemistry in the Y_2O_3–Al_2O_3–SiO_2 system , 1999 .

[19]  Y. Murakami,et al.  Crystal structure and thermal expansion of Ca2Y2Si2O9 , 1998 .

[20]  H. Wadley,et al.  Reactive vapor deposition of metal oxide coatings , 2001 .

[21]  A. J. Fernández-Carrión,et al.  Thermal Expansion of Rare‐Earth Pyrosilicates , 2013 .

[22]  David L. Poerschke,et al.  Thermochemical compatibility of ytterbia–(hafnia/silica) multilayers for environmental barrier coatings , 2013 .

[23]  Narottam P. Bansal,et al.  Rare earth silicate environmental barrier coatings for SiC/SiC composites and Si3N4 ceramics , 2005 .

[24]  David L. Poerschke,et al.  Effects of cation substitution and temperature on the interaction between thermal barrier oxides and molten CMAS , 2015 .

[25]  D. Bish,et al.  Crystal structures and cation sites of the rock-forming minerals , 1988 .

[26]  L. Brohan,et al.  Cuspidine-like compounds Ln4[Ga2(1-x)Ge2xO7+x□1-x]O2 (Ln = La, Nd, Gd; x ≤ 0.4) , 2004 .

[27]  A. Evans,et al.  A delamination mechanism for thermal barrier coatings subject to calcium-magnesium-alumino-silicate (CMAS) infiltration , 2005 .

[28]  C. Leyens,et al.  Two-source jumping beam evaporation for advanced EB-PVD TBC systems , 2000 .