Synthesis, microstructure and thermal analysis of Gd2 O3 - HfO2 coatings

Chandan Kumar Roy, University of Texas at El Paso

Abstract

Thermal barrier coatings (TBCs) are critical for future gas turbines of advanced coal based power generation systems. The TBCs are protective layers of low thermal conductivity ceramic materials, which prevent the damage of components that are exposed to very high temperature of the hot gases. Due to increasing demand to improve the efficiency, it is necessary to find alternate TBC materials which can withstand higher temperature for longer period than state-of-art TBCs. The present study focuses on the Gd2O3 stabilized HfO2 (GSH) as a potential candidate for TBC. GSH materials were synthesized in bulk and coatings form. The Gd2O 3 content was varied in the range of 0–40 mol% in order to produce GSH materials with a variable composition. The crystal structure, surface morphology, chemical composition and elemental distribution of the GSH ceramics were investigated in detail as a function of Gd2O3 content. The GSH coatings were fabricated onto various substrates (SS 403, IN 738 and, Si) by sputter-deposition under variable substrate temperature (RT-500 °C). X-ray diffraction (XRD) analyses indicate that Gd2O3 addition stabilizes the cubic HfO2 phase. The phase transforms into fcc pyrochlore (Gd2Hf2O7) increasing Gd2O3 concentration. Scanning electron microscopy (SEM) studies indicate that the surface morphology of the GSH coatings is dependent on the growth temperature; the coatings are crystalline at 500 °C. The morphology is characterized by the triangular nano-grains. The cross-sectional imaging confirms the columnar structure of all the GSH coatings. The coatings exhibit high chemical quality. The average roughness of the coating is ∼7 nm and does not vary significantly with the Gd2O3 concentration. The durability of the GSH coatings tested by exposing to the hot gases produced by combustion of methane-air and syngas-air of various compositions indicate that the carbon deposits onto the surface. The results obtained are presented and discussed to establish a correlation between synthesis conditions, microstructure and thermal stability of the GSH coatings for TBC applications.^

Subject Area

Chemistry, Inorganic|Engineering, Mechanical

Recommended Citation

Roy, Chandan Kumar, "Synthesis, microstructure and thermal analysis of Gd2 O3 - HfO2 coatings" (2011). ETD Collection for University of Texas, El Paso. AAI1498318.
http://digitalcommons.utep.edu/dissertations/AAI1498318

Share

COinS