Interfacial failure via encapsulation of external particulates in an outward-growing thermal oxide

• Published in: Journal of power sources Vol. 196; no. 10; pp. 4686 - 4694
• Main Authors: Jung, Keeyoung, Kim, Chang-Soo, Pettit, Frederick S., Meier, Gerald H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.05.2011; Elsevier
• Subjects: Alloy powders; Applied sciences; Buckling; Chromia former; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Energy; Energy. Thermal use of fuels; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Failure; Finite element analysis; Finite element method; Fuel cells; MATERIALS SCIENCE; Numerical analysis; Oxidation; Oxides; Particulates; Platinum base alloys; Silicon dioxide; Syngas; Thermal strain; Oxidation; Numerical analysis; Finite element analysis; Chromia former; Buckling; Syngas; Numerical method; Failures; Solid oxide fuel cell; Finite element method; Ash; Coal gas; Gas turbine
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2010.12.104

[Display omitted] ► Oxide failure by inert SiO2 particles in syngas-fueled gas turbines or SOFCs. ► Observation of encapsulated SiO2 only in outward growing oxides with buckling. ► Identification of failure mechanisms using analytical and computational approaches. A Cr2O3-forming Ni-base superalloy and this alloy coated with a Pt-modified aluminide coating were exposed to SiO2 powder and cyclically oxidized at 950°C. The uncoated alloy showed a considerable amount of spallation and buckling whereas the Pt–NiAl coated alloy remained protective throughout hundred 1h-cycles. The interfacial failure is mainly ascribed to the increased thermal strain by the encapsulation of external SiO2 particulates in an outward-growing Cr2O3 layer. However, the particles were not embedded in the thermally grown oxide of the Pt–NiAl coated alloy due to the slow inward-growing characteristics of Al2O3 scales. The buckling of the Cr2O3 scale with embedded SiO2 was analyzed with (1) a classical buckling criterion using the instantaneous coefficients of thermal expansion of the constituents, and (2) finite element analyses (FEA) to estimate the local interfacial shear stresses. It turns out that the thermal strain with embedded SiO2 is larger than the experimentally determined critical thermal strain (ɛb) explaining the buckling of the oxide scale observed in the experiment. The FEA results demonstrate that local shear stresses at the metal/oxide interface are significantly amplified near the SiO2 particles showing that the buckling of oxide can be readily initiated especially in the vicinity of the embedded particles.