Influence of the grain size on CMAS attack of Sm₂Zr₂O₇ ceramic

The temperature resistance of thermal barrier coatings (TBCs) has increased with the continuous development of the aviation industry. This increase in temperature resistance has resulted in a new challenge for TBCs, namely, calcium-magnesium-aluminum-silicate (CMAS) attack. As a new generation of thermal barrier coating candidate materials, Sm₂Zr₂O₇ has good CMAS resistance properties. However, this material cannot meet the actual needs of aero-engines. Therefore, a change in the structure of Sm₂Zr₂O₇ was used to improve the CMAS resistance properties in this paper. The relationship between the grain size of the ceramic and its resistance to CMAS penetration in the microstructure was investigated in detail. Nonpressure and SPS sintering processes were used to prepare Sm₂Zr₂O₇ ceramics with different grain sizes that were then tested at high temperatures with CMAS. With the extension of penetration, the depth of CMAS penetration in microscale Sm₂Zr₂O₇ ceramics increased sharply with increasing reaction time, while the penetration depth of CMAS into nanoscale Sm₂Zr₂O₇ ceramics increased slowly. After 48 h of penetration, the penetration depth of the microscale Sm₂Zr₂O₇ ceramics was 86 μm, and the penetration depth of the nanoscale Sm₂Zr₂O₇ ceramics was only 47 μm. Compared with the microscale Sm₂Zr₂O₇ ceramics, the nanoscale Sm₂Zr₂O₇ ceramics had better CMAS resistance because the lower diffusion activation energy of the nanocrystalline grains accelerated the formation of a dense barrier layer.