Infiltration Behavior of CMAS in LZ-YSZ Composite Thermal Barrier Coatings
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https://doi.org/10.1007/s11837-020-04373-4 2020 The Minerals, Metals & Materials Society
ADVANCES IN THE CIRCULAR ECONOMY OF LANTHANIDES
Infiltration Behavior of CMAS in LZ-YSZ Composite Thermal Barrier Coatings GUANLIN LYU,1 DOWON SONG,2 BAIG-GYU CHOI,3 and YEON-GIL JUNG 1,4 1.—School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 51140, Republic of Korea. 2.—Department of Energy Engineering, Hanyang University, Seoul 133-791, Republic of Korea. 3.—High Temperature Materials Research Group, Korea Institute of Materials Science, 797 Changwondaero, Changwon, Gyeongnam 641-831, Republic of Korea. 4.—e-mail: [email protected]
Calcium magnesium alumina-silicate (CMAS) corrosion on thermal barrier coatings (TBCs) is one of the reasons for the early delamination of TBCs. In this study, the effects of CMAS on the microstructure evolution of TBCs were investigated for yttria-stabilized zirconia (YSZ), lanthanum zirconate (LZ), and composite coating with a 50:50 volume ratio of LZ and YSZ (LZ-YSZ). The LZ showed the mitigated penetration of CMAS by the formation of the reaction products produced by the high reactivity between the LZ and the molten CMAS. The LZ-YSZ showed a denser microstructure on the surface, resulting in retarding the penetration of CMAS. Therefore, the LZ-YSZ composite TBC is expected to prolong the lifetime performance and protect against further corrosive degradation of TBCs in high-temperature environments. The infiltration behavior and reaction mechanism of molten CMAS were discussed based on the microstructures after the corrosion test.
INTRODUCTION Thermal barrier coatings (TBCs) are widely used in aircraft engines and gas turbines to protect metallic components from high-temperature service environments.1,2 The components with TBCs have allowed operation in a higher temperature environment with increasing turbine inlet temperature to improve fuel efficiency.3 Currently, state-of-the-art TBCs are based on 6–8 wt.% yttria-stabilized zirconia (YSZ) in the hot section parts of turbine engines. The general phase of YSZ-TBC prepared using the air plasma spraying (APS) method mainly consists of nontransformable tetragonal (t¢), tetragonal (t), and cubic (c) phases. The t¢-phase of YSZ transforms into t- and/or c-phases during long-term thermal exposure (> 1200C), and the t-phase transforms into the monoclinic (m) phase with 3–5% volume expansion.4,5 YSZ is widely employed for TBC materials because of its outstanding mechanical properties, derived from a unique ferroelasticity, resulting in the prevention of crack propagation and (Received May 12, 2020; accepted September 1, 2020)
resistance to foreign object damage.6,7 To meet the requirements mentioned, lanthanum zirconate (La2Zr2O7, LZ) with a pyrochlore (p) structure has been investigated as one of the promising candidate materials for next-generation TBCs. Compared with YSZ, LZ has a significantly lower thermal conductivity of 1.5–1.8 W m1 K1 in bulk form at 1000C, no phase transformation until
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