Inhibition of metastable alumina formation on Fe-Cr-Al-Y alloy fibers at high temperature using titania coating

Fe - Cr - Al - Y fine fibers suffer from intensive whisker formation, which is due to fast-growing meta-stable phases such as gamma or theta alumina at about 800 - 900degreesC. To inhibit the fast growth of meta-stable alumina phases, a thin layer of sol - gel titania was deposited on the fibers. The oxidation kinetics were recorded and compared between uncoated and coated samples. The scale morphology was studied by scanning electron microscopy (SEM). The scale cross section were examined using focused ion beam ( FIB). The phases of the titania coating were examined by Raman spectroscopy. It was found that at 915degreesC, titania greatly inhibits the formation of meta-stable alumina. No whiskers were found on the surface of the fibers compared to uncoated samples. The weight gain for titania-coated sample is almost one half during the first 50 hr compared to the uncoated sample at 915degreesC. The scales on the coated sample is much thinner and fewer cracks were found at the scale and alloy interface. The inhibition mechanism is discussed briefly.