Oxidation-induced failure of thermal barrier coatings. Annual report, 1 October 1997--31 October 1998

Technical Report · Tue Dec 01 04:00:00 EST 1998

OSTI ID:350692

Clarke, D R

On prolonged high-temperature exposure in air, thermal barrier coatings (TBCs) on bond-coated superalloys fail by spalling. The author has focused on identifying the underlying mechanisms of failure and sought to establish whether it is a direct consequence of the failure of the underlying thermally grown oxide. He has discovered a new TBC failure mode, one in which failure is associated with moisture-enhanced sub-critical crack-growth along the bond-coat/thermally grown oxide interface. New insights into the mechanism underlying failure of the thermally grown oxide have come from direct optical microscopy. These indicate that failure is associated with surface roughness of the bond-coat and specifically that the thermally-grown oxide separates from the bond-coat on cooling at the concave (`crests`) surface features. These locally separated regions grow with oxidation time and are seen to link-up. These events are believed to be the precursor events that grow to provide the critical-sized flaws from which buckling and spalling of thermal barrier coatings occur.

• Research Organization: California Univ., Coll. of Engineering, Santa Barbara, CA (United States)
• OSTI ID: 350692
• Report Number(s): AD-A--360036/XAB; CNN: Contract N00014-97-1-0190
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CERAMICS
CRACK PROPAGATION
FAILURES
FRACTURE MECHANICS
OXIDATION
PROTECTIVE COATINGS
SURFACE PROPERTIES
TEMPERATURE RANGE 0400-1000 K