Sulfidation Behavior of a Thermal Barrier Coating at 1173 K in H_2S-H_2 Gas Mixture with a 10~(-0.65) Pa Sulfur Partial Pressure

摘要

Sulfidation behavior of a thermal barrier coating consisted of CoNiCrAlY and YSZ (ZrO_2-8 mol percent Y_2O_3) coating, prepared by low pressure and air plasma sprayings, respectively, on a nickel based heat resistant alloy was investigated in a H_2S-H_2 atmosphere with a 10~(0.65) Pa sulfur partial pressure at 1173 K for 43.2 ks. The corrosion product with a network structure was identified by X-ray diffraction and electron probe microanalyses to be Zr_3Y_4S_(3.5)O_(9.4), which was formed from the Zr_3Y_4O_(12) by replacement of oxygen by sulfur, having the elongated c-axis and the shrunken a-axis in contrast to those of the Zr_3Y_4O_(12). 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.