Mechanisms of cracking and delamination within thick thermal barrier systems in aero-engines subject to calcium-magnesium-alumino-silicate (CMAS) penetration

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 490; no. 1; pp. 26 - 35
• Main Authors: Krämer, S., Faulhaber, S., Chambers, M., Clarke, D.R., Levi, C.G., Hutchinson, J.W., Evans, A.G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.08.2008; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cracking; Delamination; Environmental degradation; Exact sciences and technology; Fatigue, brittleness, fracture, and cracks; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Physics; Thermal barrier coatings; Thermal gradients; Thermal barrier coatings; Cracking; Delamination; Environmental degradation; Thermal gradients; Temperature gradients; Self consistency; Residual stresses; Elastic deformation; Calcium silicate; Cracks; Aluminium silicate; Magnesium silicate; CMA; Melts
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2008.01.006

An analysis has been conducted that characterizes the susceptibility to delamination of thermal barrier coated (TBC) hot-section aero-turbine components when penetrated by calcium-magnesium-alumino-silicate (CMAS). The assessment has been conducted on stationary components (especially shrouds) with relatively thick TBCs after removal from aero-engines. In those segments that experience the highest temperatures, the CMAS melts, penetrates to a depth about half the coating thickness, and infiltrates all open areas. Therein the TBC develops channel cracks and sub-surface delaminations, as well as spalls. Estimates of the residual stress gradients made on cross-sections (by using the Raman peak shift) indicate tension at the surface, becoming compressive below. By invoking mechanics relevant to the thermo-elastic stresses upon cooling, as well as the propagation of channel cracks and delaminations, a scenario has been presented that rationalizes these experimental findings. Self-consistent estimates of the stress and temperature gradients are presented as well as predictions of channel cracking and delamination upon cooling.