Thermal cycle and water oxygen performance of multi-layered Y3Al5O12/Yb2SiO5/Yb2Si2O7 thermal/environmental barrier coatings

Abstract

In this work, the Y3Al5O12 (YAG) coatings prepared by atmospheric plasma spraying were found to have a thermal expansion coefficient of 8.51 × 10-6K-1 from 473 to 1673K and a thermal conductivity of 2.41 W/(m∙K) at 1273K as well as a Young's modulus of 89.4 ± 9 GPa and an average hardness of 6.79 ± 0.24 GPa. Their excellent mechanical and thermal-physical properties have promoted them as thermal/environmental barrier coating (T/EBC) materials. Multi-layered Y3Al5O12/Yb2SiO5/Yb2Si2O7 (YAG/YbMS/YbDS) T/EBCs were deposited on SiC based substrate. Thermal cycling and water vapor corrosion behavior of the YAG/YbMS/YbDS T/EBCs were also investigated. The cyclic oxidation tests at 1573K showed that the coatings had excellent resistance to thermal cycling, with an average lifetime of 442 ± 10 cycles. The initial oxidation of the Si layer at the edge, resulting in the formation of a 4.8 μm thick thermally grown oxide (TGO), coupled with the volumetric changes and the associated phase transformation stress, led to the delamination of the coatings from the edges. Due to the very low oxygen diffusion rate of YAG layer, the thickness of TGO was only 1.2 μm after steam corrosion for 40 h. The amorphous crystallization as well as thermal mismatch stresses were the main reasons for the coating failure.