1. © Effect Of Platinum On The Oxide-To-Metal Adhesion In Thermal Barrier Coating Systems Tawancy, HM; Ui-Hamid, A; Abbas, NM; Aboelfotoh, MO SPRINGER, JOURNAL OF MATERIALS SCIENCE; pp: 2978-2989; Vol: 43 King Fahd University of Petroleum & Minerals http://www.kfupm.edu.sa Summary An investigation was conducted to determine the role of Pt in a thermal barrier coating system deposited on a nickel-base superalloy. Three coating systems were included in the study using a layer of yttria-stabilized zirconia as a model top coat, and simple aluminide, Pt-aluminide, and Pt bond coats. Thermal exposure tests at 1,150 degrees C with a 24-h cycling period to room temperature were used to compare the coating performance. Additional exposure tests at 1,000, 1,050, and 1,100 degrees C were conducted to study the kinetics of interdiffusion. Microstructural features were characterized by scanning electron microscopy and transmission electron microscopy combined with energy dispersive X-ray spectroscopy as well as X-ray diffraction. Wavelength dispersive spectroscopy was also used to qualitatively distinguish among various refractory transition metals. Particular emphasis was placed upon: (i) thermal stability of the bond coats, (ii) thickening rate of the thermally grown oxide, and (iii) failure mechanism of the coating. Experimental results indicated that Pt acts as a 'cleanser' of the oxide-bond coat interface by decelerating the kinetics of interdiffusion between the bond coat and superalloy substrate. This was found to promote selective oxidation of Al resulting in a purer Al2O3 scale of a slower growth rate increasing its effectiveness as 'glue' holding the ceramic top coat to the underlying metallic substrate. However, the exact effect of Pt was found to be a function of the state of its presence within the outermost coating layer. Among the bond coats included in the study, a surface layer of Pt-rich gamma'-phase (L1(2) superlattice) was found to provide longer coating life in Copyright: King Fahd University of Petroleum & Minerals; http://www.kfupm.edu.sa

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3. 41. 42. 43. 44. © 10.1016/j.actamat.2004.07.019 WOOD JH, 1987, SUPERALLOYS, V2, P359 WU BC, 1990, MAT SCI ENG A-STRUCT, V124, P215 YANAR NM, 2003, MATER HIGH TEMP, V20, P495 For pre-prints please write to: tawancy@kfupm.edu.sa Copyright: King Fahd University of Petroleum & Minerals; http://www.kfupm.edu.sa