Effect of heat treatment on phase stability, microstructure, and thermal conductivity of plasma-sprayed YSZ
Abstract
The effects of 50-hour heat treatments at 1000°C, 1200°C, and 1400°C on air plasma-sprayed coatings of 7 wt% Y_2O_3-ZrO_2 (YSZ) have been investigated. Changes in the phase stability and microstructure were investigated using x-ray diffraction and transmission electron microscopy, respectively. Changes in the thermal conductivity of the coating that occurred during heat treatment were interpreted with respect to microstructural evolution. A metastable tetragonal zirconia phase, with a non-equilibrium amount of Y_2O_3 stabilizer, was the predominant phase in the as-sprayed coating. Upon heating to 1000°C for 50 hours, the concentration of the Y_2O_3 in the t-zirconia began to decrease as predicted by the Y_2O_3-ZrO_2 phase diagram. The c-ZrO_2 phase was first observed after the 50-hour heat treatment at 1200°C; monoclinic zirconia was observed after the 50-hour heat treatment at 1400°C. TEM analysis revealed closure of intralamellar microcracks after the 50-hour/1000°C heat treatment; however, the lamellar morphology was retained. After the 50-hour/1200°C heat treatment, a distinct change was observed in the interlamellar pores; equiaxed grains replaced the long, columnar grains, with some remnant lamellae still observed. No lamellae were observed after the 50-hour/1400°C heat treatment. Rather, the microstructure was equivalent when viewed in either plan view or cross-section, revealing large grains with regions of monoclinic zirconia. Thermal conductivity increased after every heat treatment. It is believed that changes in the intralamellar microcracks and/or interlamellar pores are responsible for the increase in thermal conductivity after the 1000°C and 1200°C heat treatments. The increase in thermal conductivity that occurs after the 50-hour/1400°C heat treatment is proposed to be due to the formation of m-ZrO_2, which has a higher thermal conductivity than tetragonal or cubic zirconia.
Additional Information
© 2002 Kluwer. Received 15 January and accepted 21 December 2001. The authors wish to thank Dr. Wen-An Chiou for assistance with the TEM. This work was supported by the U.S. Department of Energy, Federal Energy Technology Center, Cooperative Agreement No. DE-FC21-92MC29061, under subcontract 96-01-SR047. A. R. de Arellano-López was supported by the Eschbach Visiting Scholar Program of the McCormick School of Engineering and Applied Science at Northwestern University. The thermal conductivity testing was supported by the U.S. DOE, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Transportation Technologies, as part of the HTML User Program under contract DE-AC05-00OR22725, managed by UT-Batelle, LLC.Additional details
- Eprint ID
- 49384
- DOI
- 10.1023/A:1015310509520
- Resolver ID
- CaltechAUTHORS:20140908-181321645
- DE-FC21-92MC29061
- Department of Energy (DOE)
- Eschbach Visiting Scholar Program, Northwestern University
- DE-AC05-00OR22725
- Department of Energy (DOE)
- Created
-
2014-09-09Created from EPrint's datestamp field
- Updated
-
2021-11-10Created from EPrint's last_modified field