Paper Title:
Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion
  Abstract

Alumina scale adhesion on high temperature alloys is known to be affected primarily by sulfur segregation and reactive element additions. However adherent scales can become partially compromised by excessive strain energy and cyclic cracking. With time, exposure of such scales to moisture can lead to spontaneous interfacial decohesion, occurring while the samples are maintained at ambient conditions. Examples of this Moisture-Induced Delayed Spallation (MIDS) are presented for NiCrAl and single crystal superalloys, becoming more severe with sulfur level and cyclic exposure conditions. Similarly, delayed failure or Desk Top Spallation (DTS) results are reviewed for TBC’s, culminating in the water drop failure test. Both phenomena are discussed in terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment. Hydroxylization of aluminum from the alloy interface appears to be the relevant basic reaction.

  Info
Periodical
Materials Science Forum (Volumes 595-598)
Edited by
Pierre Steinmetz, Ian G. Wright, Alain Galerie, Daniel Monceau and Stéphane Mathieu
Pages
191-198
DOI
10.4028/www.scientific.net/MSF.595-598.191
Citation
J. L. Smialek, "Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion", Materials Science Forum, Vols. 595-598, pp. 191-198, 2008
Online since
September 2008
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