Al-O-N based duplex coating system for improved oxidation resistance of superalloys and NiCrAlY coatings

S. K. Jha, Y. H. Sohn, S. Sastri, N. Gunda, J. A. Haynes

Research output: Contribution to journalArticlepeer-review

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Abstract

Performance of an Al-O-N based duplex coating system (DCS) was examined in order to improve the high-temperature oxidation resistance of superalloys and the low-pressure plasma sprayed NiCrAlY coatings. The DCS (∼5 μm thick) was deposited using pulsed DC reactive magnetron sputtering as an external coating on Rene'N5 superalloy with and without NiCrAlY coating. DCS coatings were characterized using photo-stimulated luminescence spectroscopy, optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy before and after high-temperature oxidation. As-deposited DCS contained varying amounts of α-, γ-Al2O3 and amorphous phases depending on the chemistry and surface characteristics of the substrate. Heat treatment at 1121 °C (2050 °F) for 2 h in air facilitated complete phase transformation to equilibrium α-Al2O3 in the DCS. Improvement in oxidation resistance was observed for DCS specimens during 250-h oxidation at 1121 °C (2050 °F). In particular, DCS was found to be very effective as an external coating on the rough (as-sprayed) NiCrAlY surface. The superior oxidation resistance of the specimens with DCS may be attributed to the formation of slow-growing and adherent alumina scale and the prevention of Ni/Cr-rich oxide formation.

Original languageEnglish
Pages (from-to)224-232
Number of pages9
JournalSurface and Coatings Technology
Volume183
Issue number2-3
DOIs
StatePublished - May 24 2004

Keywords

  • Coatings
  • Oxidation
  • Photostimulate luminescence
  • Residual stress
  • Thermally grown oxide

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