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

Equimolar YO1.5 and TaO2.5 co‐doped ZrO2 as a potential CMAS‐resistant material for thermal barrier coatings

“…A most recently research showed that the adding of Ta 5+ in Zr 4 Y 3 O 12 could degrade the CMAS resistance, due to the suppression of the apatite precipitation 33 . It was found that the adding of Ta 5+ increases the capture of Y 3+ by the reprecipitated fluorite, decreasing the Y 3+ amount available to form apatite 33 . In view of precipitation of apatite, the adding of Ta 5+ in ZrO 2 ‐YO 1.5 binary system has detrimental effects on the CMAS resistance.…”

“…33 It was found that the adding of Ta 5+ increases the capture of Y 3+ by the reprecipitated fluorite, decreasing the Y 3+ amount available to form apatite. 33 In view of precipitation of apatite, the adding of Ta 5+ in ZrO 2 -YO 1.5 binary system has detrimental effects on the CMAS resistance. However, our study shows that for ZYTO, although the formation of apatite is also inhibited, the other reliable reaction product (YO 1.5 /TaO 2.5 /CaO codoped ZrO 2 , product #2) is precipitated, which can form the dense product layer like apatite and effectively inhibit the further infiltration/corrosion of CMAS melt ( Figure 4D).…”

“…2) From the CMAS resistance viewpoint, previous studies suggest that the CMAS reactivity with ZrO 2 -based oxides is strongly dependent on the initial rare earth oxides (REO 1.5 ) content. [33][34][35] The high dopant content in ZYTO, that is, 17 mol% YO 1.5 + 17 mol% TaO 2.5 , implies that ZYTO may react with CMAS melt and precipitate as reaction products easily to mitigate further CMAS infiltration. Here, we performed systematically experimental studies on the CMAS resistance of ZYTO, and compared with 17 mol% YO 1.5 -doped ZrO 2 (17YSZ).…”

“…1) From the viewpoint of thermal and mechanical properties, ZYTO has low thermal conductivity (~1.5 W.m ‐1 .K ‐1 ), compatible CTE with the thermally grown oxide (TGO) (~11.2 ppm.K ‐1 ), high‐fracture toughness (3‐4 MPa.m ‐1/2 ), and high‐temperature stability (ie, ZYTO can retain the tetragonal crystal structure up to 1500°C), 28‐32 which are ideal for TBCs application. 2) From the CMAS resistance viewpoint, previous studies suggest that the CMAS reactivity with ZrO 2 ‐based oxides is strongly dependent on the initial rare earth oxides (REO 1.5 ) content 33‐35 . The high dopant content in ZYTO, that is, 17 mol% YO 1.5 + 17 mol% TaO 2.5 , implies that ZYTO may react with CMAS melt and precipitate as reaction products easily to mitigate further CMAS infiltration.…”

Garnet stability in the Al–Ca–Mg–Si–Y–O system with implications for reactions between TBCs, EBCs, and silicate deposits

“…(20)(21)(22) CMAS deposits containing larger fractions of MgO, Fe 2 O 3 and Al 2 O 3 appear to promote the formation of aluminosilicate garnet solid solutions at the expense of apatite crystallization, particularly for coatings based on the smaller RE cations (e.g., Yb 3+ or Y 3+ , compared to Gd 3+ , Nd 3+ , or La 3+ ). (8,15,30,17,(23)(24)(25)(26)(27)(28)(29) Interactions of titania and iron oxide rich CMAS with YSZ coatings has shown the formation of kimzeyite type garnets. (31,32) There is evidence that the shift from apatite formation to garnet formation negatively affects coating durability due to slower crystallization kinetics (for TBCs) or the generation of proportionally larger volume of the CTEmismatched phases per mole of coating dissolved (for EBCs).…”