Investigation on the phase stability, sintering and thermal conductivity of Sc2O3–Y2O3–ZrO2 for thermal barrier coating application

2014

Adv Eng Mater

Thermal barrier coatings (TBCs) made of low-thermal conductivity oxide ceramics are applied to the surfaces of metallic parts in the hottest sections of advanced gas-turbine engines, to reduce the underlying superalloy temperature and to increase the turbine efficiency. [1,2] The most practical TBCs currently are ZrO 2 -based having a composition containing 4 mol% Y 2 O 3 (4YSZ), due to its low thermal conductivity, high thermal expansion coefficient (TEC), and high fracture toughness in the metastable tetragonal (t 0 ) structure. [3][4][5][6] However, the long-time exposure of 4YSZ at temperatures higher than 1200°C will lead to a partitioning of the t 0 phase to tetragonal (t), and cubic (c) phases. On cooling, the t phase occurs a martensitic transformation to monoclinic (m) phase, resulting in a volume increase of 4 vol%. [7] The stress resulting from the volumetric change gives rise to the formation of cracks in the ceramic, contributing to the spallation of the coatings. [8,9] There is a worldwide search under way for oxide ceramics with superior thermophysical properties that could replace 4YSZ. One strategy for developing next-generation TBC materials is to use rare-earth oxides (RE 2 O 3 ) as alternative stabilizers to Y 2 O 3 for ZrO 2 -based systems. Recent works have shown that ZrO 2 stabilized with Nd

Section: Resultssupporting

confidence: 93%

mentioning

confidence: 99%

Thermophysical Properties and Sintering of Ytterbia‐Stabilized Tetragonal Zirconia Ceramic

2014

Adv Eng Mater

“…The use of rare‐earth oxides (such as Nd 2 O 3 , Gd 2 O 3 , Yb 2 O 3 and Sc 2 O 3 ) as an alternative stabilizer to Y 2 O 3 in ZrO 2 ‐based materials has been conducted for many years . Unfortunately, these stabilizers actually decrease the resistance to destabilization of the t ′‐ZrO 2 structure except for Yb 2 O 3 .…”

Section: Introductionmentioning

confidence: 99%

Effect of High‐Temperature Aging on the Fracture Toughness of 40 mol% Ceria‐Stabilized Zirconia

2014

J. Am. Ceram. Soc.

The 40 mol% CeO 2 -stabilized ZrO 2 ceramic was synthesized by the sol-spray pyrolysis method and aged at 1400°C-1600°C. The effects of high-temperature aging on its fracture toughness were investigated after heat treatments at 1500°C for 6-150 h in air. Characterization results indicated that the activation energy for grain growth of 40 mol% CeO 2 -stabilized ZrO 2 was 593 AE 47 kJ/mol. The average grain size of this ceramic varied from 1.4 to 5.6 lm within the aging condition of 1500°C for 6-150 h. The Ce-lean tetragonal phase has a constant tetragonality (ratio of the c-axis to a-axis of the crystal lattice) of 1.0178 during the aging process. It was found that the fracture toughness of 40 mol% CeO 2 -stabilized ZrO 2 was determined to be 2.0 AE 0.1 MPaÁm 1/2 , which did not vary significantly with prolonging aging time. Since no monoclinic zirconia was detected in the regions around the indentation crack-middle and crack-tip, the high fracture toughness maintained after high-temperature aging can be attributed to the remarkable stability of the tetragonal phase in 40 mol% CeO 2 -stabilized ZrO 2 composition.R. Trice-contributing editor Manuscript No. 34951.

“…It is expected that the complete breakdown of the t′ phase would lead to an equilibrium state between the t and c phases under the extreme service condition, resulting in a constant value for the m phase content at room temperature. Some experimental evidence has shown that the relative content of m phase in YSZ kept constant after annealing at 1500°C for 100–300 h . However, the effects of RE 3+ ions on m phase content under equilibrium conductions have received much less attention.…”

Section: Introductionmentioning

confidence: 99%

Effects of RE³⁺ Ionic Radius on Monoclinic Phase Content of 8 mol% REO_1.5 Partially Stabilized ZrO₂ (RE = Yb, Y, Gd, and Nd) Powder Compacts after Annealing at High Temperature

et al. 2013

J. Am. Ceram. Soc.

Powders of zirconia doped with 8 mol% REO 1.5 (RE = Yb, Y, Gd, and Nd) were synthesized by using the sol-spray pyrolysis method. The effects of RE 3+ ionic radius on monoclinic (m) phase content of powders were investigated. The XRD results showed that the metastable tetragonal (t′) phase underwent a complete phase change to form m and cubic (c) phases after a heat treatment of 50-100 h at 1450°C. A cation size-dependent reduction in the m phase content of the REO 1.5 partially stabilized ZrO 2 powders was observed. The SEM-EDS analysis of the powders revealed that the RE 3+ concentrations in the c phases decreased with decreasing the RE 3+ ionic radius. These results indicate that the stabilizer concentration of the c phase can be attributed to RE 3+ ionic radii, resulting in different m phase contents. Compared to the REO 1.5 single doped ZrO 2 , the m phase contents of 8 mol% (RE 0.5 Yb 0.5 )-ZrO 2 (RE = Y, Gd, and Nd) powders were significantly reduced. The results prove that the stabilizer with a lower RE 3+ size is effective in reducing the m phase content of partially stabilized ZrO 2 after annealing at high temperatures.