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

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 LaMgAl 11 O 19 (LMA) TBC and Yb 2 Si 2 O 7 (YbDS) EBC, a transition layer formed by positive thermal-expansion LMA and negative thermal-expansion LiAlSiO 4 (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. • LMA (positive CTE)-LAS (negative CTE) composite coating was used as transition layer between LMA-TBC and YbDS-EBC layer. • LMA-LAS possessed excellent fracture toughness of 1.60 MPa m 1/2 and intermediate CTE of ~6.65 × 10 −6 K −1 . • Thermal cycling lifetime of LMA/YbDS/Si T/EBCs was improved by 20 % with LMA-LAS transition layer. Note: LMA = LaMgAl 11 O 19, LAS = LiAlSiO 4, YbDS = Yb 2 Si 2 O 7 TBC = Thermal barrier coating, EBC = Environmental barrier coating CTE = Coefficient of thermal expansion