Microstructural Modifications and Failure Mechanisms of an Aluminum‐Based Abradable Coating System during Isothermal and Cyclic Aging

• Published in: Advanced engineering materials Vol. 26; no. 15
• Main Authors: Prillieux, Aurélien, Thouron, Carole, Josse, Claudie, Proietti, Arnaud, Julien, Gurt‐Santanach, Fabrice, Crabos, Benoit, Malard
• Format: Journal Article
• Language: English
• Published: 01-08-2024
• Subjects: Al‐Si abradable coating; failure mechanism; Ni‐Al bond‐coat; phase transformation
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.202400118

Abradable systems are used in the aeronautical industry to improve the efficiency of gas turbine. Those materials are exposed in service to temperature up to 450 °C. The increase in gas turbine efficiency requires to increase the operating temperature and therefore the service temperature of abradable coating. The present study focuses on the isothermal and cyclic thermal aging of the Al–Si abradable coating system in a laboratory air at high temperature up to 500 °C. The investigation encompasses the microstructural evolution, phase transformation, and the formation of cracks, along with their interrelated effects. During aging, silicon particles precipitate in the abradable top coat. In addition, coarsening of those particles is observed and the coarsening kinetics appears to be faster in cyclic thermal aging conditions compared to isothermal aging. During cyclic and isothermal aging, brittle aluminides develope at the abradable top–coat/bond–coat interface, due to the interdiffusion of Al and Ni species. During cyclic aging, thermal cycles create thermomechanical stress at the top‐coat/bont‐coat interface due to coefficient of thermal expansion mismatch between the Al‐Si deposit and intermetallic phases. The stress generated results in the formation of cracks and porosities at the top–coat/bond–coat interface resulting in a dramatic failure of the system.
The actual study on the abradable system failure deals with the phase transformation and microstructure evolution during isothermal and cyclic aging. After aging, precipitation of new phases at interfaces of the abradable system is observed, and the mismatch in the mechanical properties and the thermal expansion coefficient between the newly formed phases results in failure of the system.