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

Eeshani Godbole, Nikhil Karthikeyan, David Poerschke

Research output: Contribution to journalArticlepeer-review

Abstract

This work expands the understanding of the garnet solid solution field in the yttria-calcia-magnesia-alumina-silica system. The crystal chemistry was used to define the theoretical extent of the garnet homogeneity range based on site-specific substitution rules and charge neutrality constraints. Compositions lying within this range were equilibrated at 1400°C. The resulting phase assemblages were analyzed to determine the identity and compositions of the equilibrium phases. Quantitative chemical analysis was used to infer that Mg2+ preferentially partitions into the intermediate-sized octahedral site compared to the larger dodecahedral site, that Ca2+ has a higher solubility in the dodecahedral site than Mg2+, and that the presence of Mg2+increases the total Si4+ solubility in the garnet structure. The results were also used to map the extent of the garnet solid solution phase field at 1400°C. The findings are discussed in the context of efforts to understand the interactions between Y-containing thermal and environmental barrier coatings and silicate deposits.

Original languageEnglish (US)
Pages (from-to)5270-5282
Number of pages13
JournalJournal of the American Ceramic Society
Volume103
Issue number9
DOIs
StatePublished - Sep 1 2020

Bibliographical note

Funding Information:
This study was supported by an Office of Naval Research (ONR) funded collaboration with QuesTek Innovations monitored by Dr David Shifler (N00014‐17‐C‐2034). SEM‐EDS characterization was carried out in the Characterization Facility, University of Minnesota, a member of the NSF funded Materials Research Facilities Network ( www.mrfn.org ) supported by the MRSEC program. The Hitachi SU8230 SEM‐EDS instrument was provided by NSF MRI DMR‐1229263. The EPMA facility was supported by NSF EAR‐1625422. The authors are grateful to Drs. Carlos Levi (UCSB), Dana Frankel (QuesTek Innovations) and Weiwei Zhang (ThermoCalc Software) for helpful discussions, Dr Anette von der Handt for EPMA assistance and Uma Venkata for assistance with sample preparation.

Funding Information:
This study was supported by an Office of Naval Research (ONR) funded collaboration with QuesTek Innovations monitored by Dr David Shifler (N00014-17-C-2034). SEM-EDS characterization was carried out in the Characterization Facility, University of Minnesota, a member of the NSF funded Materials Research Facilities Network (www.mrfn.org) supported by the MRSEC program. The Hitachi SU8230 SEM-EDS instrument was provided by NSF MRI DMR-1229263. The EPMA facility was supported by NSF EAR-1625422. The authors are grateful to Drs. Carlos Levi (UCSB), Dana Frankel (QuesTek Innovations) and Weiwei Zhang (ThermoCalc Software) for helpful discussions, Dr Anette von der Handt for EPMA assistance and Uma Venkata for assistance with sample preparation.

Publisher Copyright:
© 2020 The American Ceramic Society

Keywords

  • CMAS
  • environmental barrier coatings
  • garnet
  • rare earth
  • solid solution
  • thermal barrier coatings

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