The role that bond coat depletion of aluminum has on the lifetime of APS-TBC under oxidizing conditions

• Published in: Materials and corrosion Vol. 59; no. 7; pp. 547 - 555
• Main Authors: Renusch, D., Schorr, M., Schütze, M.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.07.2008; WILEY‐VCH Verlag; Wiley-VCH
• Subjects: aluminum depletion; aluminum diffusion; Applied sciences; bond coat; Corrosion; Corrosion environments; Exact sciences and technology; Metals. Metallurgy; Nonmetallic coatings; Production techniques; spallation; Surface treatment; thermal barrier coating; Lifetime; Corrosion; Non metal coating; Thermal barrier; Surface treatment
• ISSN: 0947-5117; 1521-4176
• DOI: 10.1002/maco.200804137

Bond coat oxidation as well as bond coat depletion of Al are still believed to be a major degradation mechanism with respect to the lifetime of thermal barrier coating (TBC) systems. In this study the top coat lifetime is described as being limited by both bond coat depletion of Al and mechanical failure of the top coat. The empirical results are introduced by considering three spallation cases, namely, Al depletion failure, thermal fatigue failure, and thermal aging failure. Al depletion failure occurs when the Al content within the bond coat reaches a critical value. In this paper bond coat depletion of Al is modeled by considering the diffusion of Al into both the thermally grown oxide (TGO) and substrate. The diffusion model results are compared to Al concentration profiles measured with an electron beam microprobe. These measured results are from oxidized air plasma sprayed TBC systems (APS‐TBC) with vacuum plasma sprayed (VPS) bond coats for exposures up to 5000 h in the temperature range of 950–1100 °C. This paper focuses on the Al depletion failure and how it relates to top coat spallation.