Thermal expansion studies of electron beam evaporated yttria films on Inconel-718 substrates

In this paper, phase pure cubic yttrium oxide (Y2O3) films deposited by electron beam physical vapor deposition technique on Inconel-718 substrate at different substrate temperatures (773-973 K) are investigated. The structure and phase evolution in the films of Y2O3 as a function of substrate temperature have been evaluated by X-ray diffraction. Atomic force microscopy and scanning electron microscopy were used to examine the surface roughness and morphology of the as-deposited Y2O3 films. The adhesion behavior of the Y2O3 film with Inconel-718 substrate was investigated using scratch indentation testing. The thermal expansion coefficient (TEC) of Inconel-718 substrate and Y2O3 film coated on Inconel-718 substrate were determined by high temperature Xray diffraction (HTXRD) measurement in the temperature range of 298-1273 K with temperature interval of 100 K. The linear TECs of Inconel-718 and Y2O3 film at 1273 K were found to be 1.22 x 10(-6) K-1 and 7.02 x 10(-6) K-1, respectively. Thermal stability of the Y2O3 coated Inconel-718 substrate tested at 1273 K in air over a period of 100 h is also discussed.