Abstract
Sulfidation behavior of a thermal barrier coating consisted of CoNiCrAlY and YSZ (ZrO2-8mol%Y2O3) coating, prepared by low pressure and air plasma sprayings, respectively, on a nickel based heat resistant alloy was investigated in a H2S-H2 atmosphere with a 10-0.65Pa sulfur partial pressure at 1173K for 43.2ks. The corrosion product with a network structure was identified by X-ray diffraction and electron probe microanalyses to be Zr3Y4S3.5O9.4, which was formed from the Zr3Y4O12 by replacement of oxygen by sulfur, having the elongated c-axis and the shrunken a-axis in contrast to those of the Zr3Y4O12. Sulfur and/or hydrogen sulfide gases were assumed to diffuse through flaws such as cracks and voids across the YSZ coating and reacted with Cr to form Cr-sulfide surrounding the aluminum-rich oxide layer at the YSZ/CoNiCrAlY interface.
