The performance and reliability of thermal barrier systems are greatly affected by the behavior of their bond coats. Microsample tensile experiments conducted on commercial two-phase NiCoCrAlY bond coats have unveiled impressive room temperature strength and tensile ductility; in the as-processed state yield strengths exceeding 1200 MPa and elongations to failure of up to 0.75% plastic strain have been measured. Thermally cycled specimens show a lower yield strength of 660 MPa and up to 1.5% plastic strain. Elevated temperature microsample experiments revealed less impressive properties. Transmission electron microscopy points to the importance of nano-scale ?? precipitates as a contributor to room temperature strength. Thermal cycling has been related to a general coarsening of the microstructure and a modest reduction in room temperature strength. Thermal cycling also results in the transformation of ?-grains from an ordered B2 structure to L10 martensite, but the significance of this transformation remains to be elucidated.
Characterizing the microstructure and mechanical behavior of two-phase NiCoCrAlY bond coat for thermal barrier systems
K. J. Hemker, B. G. Mendis,
Mat. Sci. Eng. A, Band 483-484, Seiten 727-730 (2008)