Effect of microstructure on thermal shock cracking of functionally graded thermal barrier coatings studied by burner heating test

Akira Kawasaki, Ryuzo Watanabe, Masahiro Yuki, Yasumasa Nakanishi, Hisaichi Onabe

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

The thermal shock fracture mechanism of metal/ceramic functionally graded thermal barrier coatings was studied by burner heating test. Discussions were made on the basis of fracture mechanics with special reference to the effect of microstructure on crack extension behavior. Two types of FGM coatings, having the same graded structure with different microstnictures, were fabricated by slurry dipping and HIP sintering process: PSZ/TN100 FGMs having finely mixed microstructure and PSZ/Inco718 FGMs having rather coarse microstructure. The fracture toughness of each composition was determined by conventional vickers indentation method on uniform nonFGM specimens. It has been shown that the fracture toughness depends strongly on the microstructure following from the mixing conditions and the particle size of the raw material powders. In PSZ/IN100 FGMs, the fracture toughness increased with increase in the metal phase content, while in PSZ/Inco718 FGMs it was fairly lower than that of PSZ/IN100 FGMs, owing to roughly dispersed metal phase in the PSZ matrix. The results of burner heating test revealed that the crack formation was always observed on the ceramic surface during cooling. By comparison between the fracture toughness and mode I stress intensity factor, the initiated vertical cracks in PSZ/ Inco718 FGMs were considered to extend into the interface of FGM/substrate without deflection. This crack extension behavior was confirmed by observing the cross-section of the tested sapmles. Although vertical cracks in PSZ/IN100 FGMs tend to be arrested in the FGM coating, with the extension of the cracks into the graded layer, they deflected toward the direction parallel to the surface. The depth of the parallel cracks beneath the surface may correspond to a location of mode n stress intensity being equal to zero.

Original languageEnglish
Pages (from-to)788-795
Number of pages8
JournalMaterials Transactions, JIM
Volume37
Issue number4
DOIs
Publication statusPublished - 1996 Jan 1

Keywords

  • Failure mechanism
  • Fracture mechanics
  • Fracture toughness
  • Functionally graded material
  • Microstructure
  • Thermal barrier coating
  • Thermal shock cracking acoustic emission

ASJC Scopus subject areas

  • Engineering(all)

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