Transformations and cracks in zirconia films leading to breakaway oxidation of Zircaloy

Haitham El Kadiri, Z. N. Utegulov, M. Khafizov, M. Asle Zaeem, M. Mamivand, A. L. Oppedal, K. Enakoutsa, M. Cherkaoui, R. H. Graham, A. Arockiasamy

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)

Abstract

Using combined Raman spectroscopy, atomic force microscopy and optical microscopy, this paper suggests that breakaway oxidation of Zircaloy is caused by the change of circumferential stress sign from compressive to tensile, which triggers catastrophic cracks to propagate from the oxide free surface toward the oxide-metal interface. The stress sign changes at a critical oxide thickness, which depends on the circumferential stress at the interface. This biaxial interfacial stress is promoted by a lattice expansion stress that accompanies the tetragonal to monoclinic crystal phase transition. In contrast with current research in the literature, this allotropic transformation is suggested to be beneficial, not detrimental, because it contributes to retard the thresholds for the change of circumferential stress sign, and thus breakaway oxidation. The tetragonal phase was revealed to localize at the interface and adopt the shape of prismatic isosceles triangles detected at early stages of oxidation. These growth morphologies are consistent with a cationic oxidation mechanism. Upon phase transition, the monoclinic variant quickly dominates the oxide scale above the interfacial regions and forces the overall oxidation to proceed by an anionic diffusion mechanism. The results of Raman spectroscopy compared well with those of atomic force microscopy.

Original languageEnglish
Pages (from-to)3923-3935
Number of pages13
JournalActa Materialia
Volume61
Issue number11
DOIs
Publication statusPublished - Jun 2013

Keywords

  • Breakaway
  • Cracking
  • Oxidation
  • Phase transformation
  • Zirconium alloys

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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