Effects of amorphous phase on hot corrosion behavior of plasma-sprayed LaMgAl 11 O 19 coating

S. Tsukada, S. Kuroda, M. Nishijima, H. Araki, Atsushi Yumoto, M. Watanabe

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2 Citations (Scopus)

Abstract

Plasma-sprayed LaMgAl 11 O 19 (LaMA) coating as a novel thermal barrier coating candidate has been studied for more than a decade, but it tends to contain significant amounts of non-equilibrium amorphous phase due to rapid solidification. The microstructure of such as-sprayed LaMA coating was first studied in detail by a transmission electron microscope (TEM), which revealed that the coating consisted mostly of an amorphous phase but with very thin layers of crystalline (thickness ~ 100 nm) phase at the boundary of neighboring sprayed particles. A hot corrosion test was also conducted on an as-sprayed LaMA coating as well as on a fully-crystallized coating after heat treatment by a molten V 2 O 5 -Na 2 SO 4 mixture at 1100 °C. The coatings' cross sectional observation showed that the as-sprayed coating was affected over a wider area by the corrosion reaction than the crystallized coating. To clarify the intrinsic reactivity of the amorphous and crystalline LaMA phases with the molten salt, a piece of as-sprayed coating was crushed into powder, mixed with a salt, and tested at temperatures below and above the crystallization temperature. The reacted powder was analyzed by an X-ray diffractometer (XRD) to quantify the amounts of various phases in the sample as a function of time. The results revealed that the amorphous LaMA has a remarkably higher reaction rate with the molten salt than the crystalline phase. In fact, at the testing temperature of 1100 °C, corrosion of the sprayed LaMA powder proceeded much faster than crystallization, as almost 90% of LaMA was corroded within 30 min.

Original languageEnglish
Pages (from-to)95-105
Number of pages11
JournalSurface and Coatings Technology
Volume363
DOIs
Publication statusPublished - 2019 Apr 15

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Keywords

  • Hexaaluminate
  • High-resolution TEM
  • Molten salt
  • Quantitative XRD analysis
  • Thermal barrier coatings

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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