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Abstract: An in-phase stress controlled thermo-mechanical fatigue test (IP-TMF) on an electron beam physical-vapor-deposition (EB-PVD) 7-wt.% Y2O3-ZrO2-coated CoNiCrAlY bond coat, called an IN-738LC thermal barrier coating (TBC) system, was carried out. The temperature gradient in the through-thickness direction was achieved. Examination of the system's deformation behavior showed clear creep and superimposed ratcheting behaviors similar to those of the substrate superalloy tested by the same IP-TMF test. The EB-PVD TBC also follows the creep deformation behavior of the substrate. Anisotropic undulation of the thermally grown oxide (TGO) layer was observed in polished section observations. The undulation behavior appeared only perpendicular to the loading direction and was not observed parallel to the loading direction. The average compressive stress distribution of the TGO layer depends on the undulation behavior. The compressive stress parallel to the loading direction is nearly constant and the value agrees with the estimated thermal stress, while the stress in the undulating section is distributed unevenly such that the compressive stress is enhanced at the bottom of concave region. [Copyright &y& Elsevier]

This paper has clarified the anelasticity of 8Y-FSZ/α-alumina composites wherein the 8Y-FSZ phases are dispersed like islands. The amount of anelastic strain generated and the manner of anelastic deformation were compared to those of monolithic 8Y-FSZ. The anelastic strains of six kinds of 8Y-FSZ/α-alumina, as well as of monolithic 8Y-FSZ and monolithic α-alumina, were measured. The results showed that the anelastic strain was produced even in the composite where 8Y-FSZ phases existed as islands, and that the more the anelastic strain produced, the higher the volume fraction of 8Y-FSZ. In addition, the composition with a fully densified alumina phase had the effect of inhibiting anelastic strain in the 8Y-FSZ phase. [ABSTRACT FROM AUTHOR]

Abstract: The selective oxidation of specific components in alumina-forming alloy such as CoNiCrAlY under precisely regulated oxygen partial pressures () can be used to control polymorphism in Al2O3 scale formed on the alloy. Dense, smooth α-Al2O3 scale was formed rapidly by treatment at 1323K under a thermodynamically determined , where both aluminum and chromium in the alloy were oxidized and elements such as cobalt and nickel were not oxidized. By contrast, under a higher all the components in the alloy were oxidized, the transformation was obviously retarded, and (Co,Ni)(Al,Cr)2O4 was produced. [Copyright &y& Elsevier]