Interactions between zirconia–yttria–tantala thermal barrier oxides and silicate melts

Journal Article · 29 November 2019 · Acta Materialia

DOI: https://doi.org/10.1016/j.actamat.2019.11.060 · OSTI ID:1601623

Abdul-Jabbar, Najeb Mohammed  ^[1]; Fernandez, Abel N. ^[2]; Jackson, Richard Wesley ^[2]; Park, Daesung ^[2]; Summers, William D. ^[2]; Levi, Carlos G. ^[2]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of California, Santa Barbara, CA (United States)
2. Univ. of California, Santa Barbara, CA (United States)

The effects of TaO_2.5 additions to Y₄Zr₃O₁₂ (YZO) on its interactions with calcium-magnesium alumino-silicate (CMAS) melts are investigated herein. YZO is a candidate material for the protection of novel ZrO₂-YO_1.5-TaO_2.5 based thermal barrier coatings (TBCs) against CMAS attack, but thermochemical considerations dictate that YZO contain TaO_2.5 for interfacial compatibility. Oxides based on Y₄Zr_3-xTa_xO_12+0.5x (x = =0, 0.7, 1.4) were mixed with various ternary and quinary silicate compositions ranging in Ca:Si ratio from 0.35 to 1.13 and equilibrated at 1300 °C. The results show that all combinations form the desired apatite phase except for the mixture of the higher Ta⁵⁺ content with the lowest Ca:Si melt. It is found that the addition of Ta⁵⁺ increases the capture of Y³⁺ by the reprecipitated fluorite, decreasing the amount available to form apatite and eventually suppressing it at low Ca:Si. The effect is ascribed to the attractive interactions between Y³⁺ and Ta⁵⁺ in solid solution, similar to that found in tetragonal zirconia, but with concurrent incorporation of anion vacancies associated with excess Y³⁺ that stabilize the cubic form. As the Ca²⁺ content of the melt increases, so does the amount of Ca²⁺ incorporated in fluorite. The latter also interacts attractively with Ta⁵⁺ and leads to a reduction of captured Y³⁺ in fluorite as the Ca content in the reacting deposit increases. This serves to increase the amount of Y³⁺available in the melt to form apatite in TBC-CMAS interactions.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF); US Department of the Navy, Office of Naval Research (ONR)
• Grant/Contract Number: 89233218CNA000001; DMR 1720256; DMR 1105672; N00014-16-1–2702
• OSTI ID: 1601623
• Report Number(s): LA-UR-19-25329
• Journal Information: Acta Materialia, Vol. 185, Issue C; ISSN 1359-6454
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English