Phase Transformation and Lattice Parameter Changes of Non-trivalent Rare Earth-Doped YSZ as a Function of Temperature
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Phase Transformation and Lattice Parameter Changes of Non-trivalent Rare Earth-Doped YSZ as a Function of Temperature Shengli Jiang, Xiao Huang, Zhang He, and Andrew Buyers (Submitted April 30, 2017; in revised form August 27, 2017) To examine the effect of doping/co-doping on high-temperature phase compositions of YSZ, stand-alone YSZ and CeO2 and Nb2O5 co-doped YSZ samples were prepared using mechanical alloy and high-temperature sintering. XRD analysis was performed on these samples from room temperature to 1100 °C. The results show that the structure for the co-doped samples tends to be thermally stable when the test temperature is higher than a critical value. Monoclinic phase was dominant in Nb2O5 co-doped YSZ at temperatures lower than 600 °C, while for the YSZ and CeO2 co-doped YSZ, cubic/tetragonal phase was dominant in the whole test temperature range. The lattice parameters for all the samples increase with increasing test temperature generally. The lattice parameters for the two non-trivalent rare earth oxides codoped YSZ show that the lattice parameter a for the cubic phase of the Ce4+ co-doped YSZ is consistently greater than that of 7YSZ which is related to the presence of larger radius of Ce4+ in the matrix. The lattice parameters a, b, c for the monoclinic phase of Ce4+ co-doped YSZ are much closer to each other than that of the Nb5+ co-doped YSZ, indicating the former has better tendency to form cubic/tetragonal phase, which is desired for vast engineering applications. Keywords
CeO2, co-doped, Nb2O5, XRD analysis, YSZ
1. Introduction The demand for increasing gas turbine efficiency and higher firing temperature has pushed the superalloys to their upper limits of temperature capability and thermal stability. To lower the surface temperatures of gas turbine components, made of superalloys, and to prevent failure of components due to incipient melting, creep, oxidation, thermal fatigue and other modes of degradation, the application of thermal barrier coatings (TBCs) to the combustor and high-pressure turbine blades and vanes has become a necessity for modern gas turbines, in addition to complex internal cooling schemes (Ref 1). Development of TBC systems has been summarized in our work (Ref 2). Zirconia has three crystal forms according to temperature (Ref 3): 1180 C
2370 C
2680 C
Monoclinic Tetragonal Cubic Liquid 950 C
Shengli Jiang, CAS Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, PeopleÕs Republic of China and Department of Mechanical and Aerospace Engineering, Carleton University, Ottawa, Canada; Xiao Huang, Department of Mechanical and Aerospace Engineering, Carleton University, Ottawa, Canada; and Zhang He and Andrew Buyers, Canadian Nuclear Laboratories, Chalk River, ON, Canada. Contact e-mail: [email protected].
Journal of Materials Engineering and Performance
The 4% volume difference between monoclinic phase and tetragonal phase (Ref 4) wil
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