High temperature performances of abradable sealing coating for ceramic matrix composites

A study of abradable sealing coatings (ASCs) compatible with ceramic matrix composites (CMCs) is reported. Three kinds of bi-layer ASCs (YSZ, Yb 2 SiO 5 , and Yb 2 Si 2 O 7 ) with CaF 2 lubricant phase were deposited by atmospheric plasma spray (APS) technology, respectively, which possessed the capability to protect CMCs from degradation and alleviate thermal expansivity mismatch. The porosity of all three coatings was less than 10%, and theYSZ-CaF 2 and Yb 2 Si 2 O 7 -CaF 2 coatings possessed similar Rockwell hardness, which were smaller than the Yb 2 SiO 5 -CaF 2 coating. However, the Yb 2 Si 2 O 7 -CaF 2 coatings displayed excellent abradability in friction and wear tests at room temperature and 900 °C. Long-term oxidation tests were conducted at 1300 °C for 100 h, and the YSZ-CaF 2 coating cracked and spalled. The structures of the Yb 2 SiO 5 -CaF 2 and Yb 2 Si 2 O 7 -CaF 2 coatings remained intact. Ca 0.15 Zr 0.85 O 1.85 solid solution and CaSiO 3 phase were formed in YSZ-CaF 2 coating, while Ca 2 Yb 8 (SiO 4 ) 6 O 2 phase was generated in Yb 2 SiO 5 -CaF 2 and Yb 2 Si 2 O 7 -CaF 2 coatings. After thermal shock with 40 cycles at 1100 °C, the whole YSZ-CaF 2 coating spalled off, while the structure of Yb 2 SiO 5 -CaF 2 and Yb 2 Si 2 O 7 -CaF 2 coatings remained integrity with good thermal shock resistance. This study might offer new insights for the further development of ASCs suitable for CMCs.