TBC bond coat–top coat interface roughness: Influence on fatigue life and modelling aspects

• Published in: Surface & coatings technology 2013-12, Vol.236, p.230-238
• Main Authors: Eriksson, Robert, Sjöström, Sören, Brodin, Håkan, Johansson, Sten, Östergren, Lars, Li, Xin-Hai
• Format: Article
• Language: English
• Subjects: Applied sciences; Bonding; Coating; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Interface; Interface roughness; Materials science; Mathematical models; Metals. Metallurgy; Modelling; Nonmetallic coatings; Physics; Production techniques; Roughness; Surface treatment; Surface treatments; TBC; TECHNOLOGY; TEKNIKVETENSKAP; Thermal barrier coating; Thermal cycling fatigue; Thermal fatigue
• ISSN: 0257-8972; 1879-3347; 1879-3347
• DOI: 10.1016/j.surfcoat.2013.09.051

Thermal barrier coatings (TBCs), when used in gas turbines, may fail through thermal fatigue, causing the ceramic top coat to spall off the metallic bond coat. The life prediction of TBCs often involves finite element modelling of the stress field close to the bond coat/top coat interface and thus relies on accurate modelling of the interface. The present research studies the influence of bond coat/top coat interface roughness on the thermal fatigue life of plasma sprayed TBCs. By using different spraying parameters, specimens with varying interface roughnesses were obtained. During thermal cycling it was found that higher interface roughness promoted longer thermal fatigue life. The interfaces were characterised by roughness parameters, such as Ra, Rq and R∆q, as well as by autocorrelation, material ratio curves and slope distribution. The variation of spray parameters was found to affect amplitude parameters, such as Ra, but not spacing parameters, such as RSm. Three different interface geometries were tried for finite element crack growth simulation: cosine, ellipse and triangular shapes. The cosine model was found to be an appropriate interface model and a procedure for obtaining the necessary parameters, amplitude and wavelength, was suggested. The positive effect of high roughness on life was suggested to be due to a shift from predominantly interface failure, for low roughness, to predominantly top coat failure, for high roughness. •The influence of interface roughness on the fatigue of TBC was studied.•High interface roughness promoted longer TBC fatigue life.•The interface was characterised by roughness parameters.•The interface can be accurately modelled as a cosine wave during FE modelling.•Longer life for higher roughness was caused by larger fraction top coat fracture.