Evaluation of Microstructural Evolution of Nanostructured Yttria-stabilized Zirconia During Sintering Using Impedance Sp
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JTTEE5 21:1076–1082 DOI: 10.1007/s11666-012-9787-5 1059-9630/$19.00 Ó ASM International
Evaluation of Microstructural Evolution of Nanostructured Yttria-stabilized Zirconia During Sintering Using Impedance Spectroscopy Chenchen Ge, Liyong Ni, and Chungen Zhou (Submitted February 13, 2012; in revised form March 25, 2012) A non-destructive evaluation (NDE) technique of impedance spectroscopy (IS) was employed for studying the sintering process of nanostructured yttria-stabilized zirconia (YSZ) after exposure at 1100 °C in air for different times. The variations within microstructure of YSZ were correlated with the EIS parameters. The results showed that the resistance and capacitance of YSZ grains (g) and grain boundaries (gb) varied with the sintering time. The resistance of YSZ g and gb increased significantly in 10 h, which may correspond to closure of pores. While during the stage from 10 to 200 h, the resistance of the g was basically consistent, and the gb decreased with the growth of g, which indicated that the gb resistance was more sensitive to grain size. The change of porosity and pore shape could be interpreted through impedance parameters. The porosity decreased and the shape of pores became smaller and rounder with the increasing sintering time.
Keywords
grain growth, impedance spectroscopy, nanostructured thermal barrier coating, pores
1. Introduction Thermal barrier coatings (TBCs) have been widely used in the hot sections of gas turbines as they provide the potential to raise efficiency and operating time of the devices (Ref 1, 2). A typical duplex TBC system is composed of a heat-insulating ceramic top coating and an oxidation-resistant metallic bond coating. ZrO2 partially stabilized Y2O3—yttria-stabilized zirconia (YSZ)—is commonly used as ceramic top coat because of its low thermal conductivity and high coefficient of thermal expansion. The YSZ is generally deposited by air plasma spraying (APS), or electron beam physical vapor deposition (Ref 3). Nanostructured YSZ coatings have recently drawn much attention because of their outstanding properties. It has been confirmed (Ref 4-7) that nanostructured YSZ coatings have lower thermal conductivity, higher coefficient of thermal expansion, and more excellent mechanical properties compared with traditional YSZ coatings.
Chenchen Ge, Liyong Ni, and Chungen Zhou, Department of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Key Laboratory of Aerospace Materials and Performance (Ministry of Education), Beijing 100191, China. Contact e-mail: [email protected].
1076—Volume 21(5) September 2012
However, the grain growth and the closure of pores would occur during sintering, consequently leading to the disappearance of the nanostructure and superior properties. Thus, it is important to develop a non-destructive evaluation (NDE) method to monitor the microstructural evolution of the nano-TBCs during thermal exposure. At present, impedance spectroscopy (IS) has been used to study the degradation of ceramic materia
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