Microstructure and thermophysical properties of CeO 2 -doped SmTaO 4 ceramics for thermal barrier coatings
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Microstructure and thermophysical properties of CeO2doped SmTaO4 ceramics for thermal barrier coatings Ying Zhou1,2,a)
, Guoyou Gan1, Zhenhua Ge1, Peng Song1, Jing Feng1
1
Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, People’s Republic of China Yunnan Provincial Academy of Science and Technology, Kunming 650093, People’s Republic of China a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 18 September 2019; accepted: 2 January 2020
SmTaO4 ceramics have excellent high-temperature phase stabilities and mechanical properties and show great potential for use as next-generation thermal barrier coating (TBC) materials. CeO2–SmTaO4 ceramics are prepared via high-temperature solid–state reaction. It retains a single monoclinic phase structure. Ce4+ was reduced to Ce3+ by high-temperature deoxidation, and the Ce3+ ions substitute for an equal number of Sm3+ ions. The CeO2–SmTaO4 ceramics had lower thermal conductivities [1.09–2.75 W/(m K)] than yttria-stabilized zirconia (YSZ) [2.1–2.7 W/(m K)] at 100–800 °C, which decreased dramatically with increasing temperature. SmTaO4 doped with 2% CeO2 had lower thermal conductivity [1.09 W/(m K), 800 °C] than SmTaO4 [1.42 W/(m K), 800 °C] and 2% ZrO2-doped SmTaO4 ceramics [1.22 W/(m K), 800 °C]. The low thermal conductivity is attributed to Ce3+ substitution for an equal number of Sm3+ ions, and because Ce3+ ions are the strongest phonon scattering centers, they can decrease the phonon mean free path effectively. The thermal expansion coefficient of 8% CeO2–SmTaO4 ceramics is approximately 10.3 × 10−6 K−1 at 1200 °C, which is slightly higher than that of both YSZ (10.0 × 10−6 K−1) and SmTaO4 (9.58 × 10−6 K−1). The outstanding thermophysical properties indicate that CeO2–SmTaO4 ceramics are potential TBC materials.
Introduction Thermal barrier coatings (TBCs) constitute one of the most important material systems applied to metallic surfaces operated at elevated temperatures, such as gas turbines or aeroengine parts, to protect these devices from high-temperature oxidation and corrosion, and thereby improve the durability, fuel efficiency, and thrust weight ratio of these devices [1, 2]. The advantages of TBC materials include high melting point, excellent high-temperature phase stability, low thermal conductivity, excellent corrosion resistance, similar thermal expansion match with a bond coat, and high fracture toughness [3, 4]. The difference in thermal expansion between TBCs, bonding layer, and alloy matrix causes spalling failure in coatings. The high thermal expansion coefficient (TEC) helps in prolonging the service life of TBCs. Yttria-stabilized zirconia (YSZ) has been widely used for high-temperature TBCs, but it transforms into cubic (c) and tetragonal (t) phases above 1200 °C, with the latter being susceptible to martensitic transformation to the monoclinic phase (m), forming cracks
ª Materials Research Society 2020
in the coating [5, 6]. Increasing the operating temperatur
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