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XRD analysis of ex-service coating D3587

XRD analysis of ex-service coating D3587. 1c. The top clean side of the coating doesn’t show traces of foreign phases The top dirt side of the coating shows the presence of mainly CMAS and CaSO 4 , but also traces of some other phases

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XRD analysis of ex-service coating D3587

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  1. XRD analysis of ex-service coating D3587

  2. 1c The top clean side of the coating doesn’t show traces of foreign phases The top dirt side of the coating shows the presence of mainly CMAS and CaSO4, but also traces of some other phases The dirt bottom side of the coating shows traces of NiO which are not found in the bottom clean side In the top clean side of the coating, t´-YSZ was completely decomposed into t-YSZ and c-YSZ In the top dirt side of the coating the decomposition is not complete In the bottom clean side of the coating some decomposition occurred indicating that this part was exposed to high temperatures

  3. 1c clean side • The average amount of Y2O3 in the coating is estimated from the cell dimensions of the different phases and their proportions. Results are: • - 10.5 wt% of Y2O3 at the outer surface (clean and dirt side) • 8 wt% of Y2O3 at the inner surface (clean and dirt side) • The Y2O3 content is clearly overestimated at the outer surface because of the high amount of c-YSZ • There is no trace of foreign phases indicating that they completely reacted with t´-YSZ possibly because of the high temperature reached by this part of the coating • The temperature of the inner surface can be estimated being in the range 1000-1100 ºC for ~1000 h or even higher but for shorter time

  4. 1c dirt side The peaks of CaTiO3 and NaCO3 could be attributed to other possible phases. To assign unambiguously the peaks, we need more information (EDX, chemical analysis…) The temperature at the inner surface of the coating was quite low as can be seen from the phase content showing nearly no degradation The Y2O3 content is clearly overestimated at the outer surface (10.5 wt%) because of the high amount of c-YSZ c-YSZ is probably formed by a reaction between t´-YSZ and some foreign phases leading to the incorporation of elements stabilizing the cubic phase (Ca, Mg, Al, Si, ?)

  5. 1b Both top sides of the coating show the presence of mainly CaSO4 and MgAl2O4 The bottom sides of the coating show traces of NiO In the top clean side of the coating, t´-YSZ was partially decomposed into t-YSZ and c-YSZ XRD pattern from thr top dirt side of the coating does not indicate decomposition of t´-YSZ

  6. 1b clean side The outer surface is not contaminated by CMAS but mainly by Spinnel (MgAl2O4) and Anhydrite (CaSO4) The temperature at the inner surface of the coating was quite low as can be seen from the phase content showing nearly no degradation The amount of Y2O3 at the outer surface can be estimated ~8.5 wt% which is a little bit too high indicating the probable incorporation of foreign elements stabilizing the c-YSZ phase The temperature at the outer side of the coating can be estimated being in the range 1000-1100 ºC for ~1000 h or even higher but for shorter time

  7. 1b dirt side The outer surface is not contaminated by CMAS but mainly by Spinnel (MgAl2O4) and Anhydrite (CaSO4) The temperatures at the inner and outer surfaces of the coating were quite low as can be seen from the phase content showing nearly no degradation

  8. 1a Both top sides of the coating show the presence of mainly CaSO4 and MgAl2O4 The bottom sides of the coating show traces of NiO XRD patterns from the top sides of the coating does not indicate decomposition of t´-YSZ

  9. 1a clean side The outer surface is not contaminated by CMAS but mainly by Spinnel (MgAl2O4) and Anhydrite (CaSO4) The temperature at the inner and outer surfaces of the coating were quite low as can be seen from the phase content showing nearly no degradation

  10. 1a dirt side The outer surface is not contaminated by CMAS but mainly by Spinnel (MgAl2O4) and Anhydrite (CaSO4) The temperature at the inner and outer surfaces of the coating were quite low as can be seen from the phase content showing nearly no degradation

  11. Conclusions: • The coating 1c was exposed to high temperatures probably above 1100ºC at his outer surface and also at the inner surface indicating that this part of the coating had not a good thermal contact with its substrate before failure occurred • The coatings 1a and 1b remained in good thermal contact with the substrate before failure occurred • Traces of NiO can be observed on the inner side of 1a and 1b coatings, but not on the inner side of 1c coating whose pattern consists only of peaks associated to YSZ phases • High amounts of CMAS are only observed in the 1c part of the coating • The 1c part of the coating could be one part were the failure occurred early, exposing the neighboring parts of the substrate to corrosive products that degraded the bond-coat leading to the expansion of the failure zone • It is not yet clear if the failure of the 1c part is the results of the reaction between CMAS (Spinnel and anhydrite) with t´-YSZ leading to the transformation t´-YSZ → c-YSZ or if this reaction comes from an original bad thermal contact in this part of the coating

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