Spalling failure of a thermal barrier coating associated with aluminum depletion in the bond-coat
✍ Scribed by E.A.G Shillington; D.R Clarke
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 800 KB
- Volume
- 47
- Category
- Article
- ISSN
- 1359-6454
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✦ Synopsis
AbstractÐA plasma-sprayed thermal barrier coating is observed to spall after oxidation at 11218C from a CoNiCrAlY bond-coated superalloy at the interface between the thermally grown oxide (TGO) and the zirconia thermal barrier coating (TBC). Phase characterization by photostimulated luminescence and X-ray diraction, as well as microstructural characterization by scanning electron microscopy, indicates that the spalling is associated with the conversion of the initially formed a-alumina thermally grown oxide to achromia and a goxi grel spinel. It is proposed that the phase conversion occurs after the alumina TGO has cracked on thermal cycling and the underlying bond-coat alloy is depleted of aluminum with concurrent enrichment of the oxide by Cr, Co and Ni. The observations suggest that monitoring the luminescence intensity as a function of oxidation time might form the basis of a nondestructive tool for detecting the onset of failure based on the disappearance of a-alumina.