Thermal shock behavior of LaMgAl11O19/Yb2Si2O7/Si thermal/environmental barrier coatings with LaMgAl11O19-LiAlSiO4 transition layer

Abstract

Thermal/environmental barrier coatings (T/EBCs) could be used to protect SiC-based ceramic matrix composites (CMCs) from chemical attack and lower the substrate temperature for improving their lifetime. To mitigate the mismatch of thermal expansion coefficient (CTE) between LaMgAl11O19 (LMA) TBC and Yb2Si2O7 (YbDS) EBC, a transition layer formed by positive thermal-expansion LMA and negative thermal-expansion LiAlSiO4 (LAS) was introduced. Thermo-mechanical performance of LMA-LAS composite coating was studied. LMA-LAS composite coating exhibited an intermediate CTE and an excellent fracture toughness, revealing that LMA-LAS coating was an acceptable transition layer. Thermal shock behavior of LMA/YbDS/Si without and with LMA-LAS transition layer were compared. The thermal cycling lifetime of T/EBC was improved by about 20% with LMA-LAS intermediate layer. The final failure of T/EBC coating system was mainly associated with thermal mismatch and thermally grown oxide (TGO) formation.