Abstract:The thermal and environmental barrier coatings were deposited on SiCf/SiC composites using atmospheric plasma spraying. The thermal conductivity of the coatings was measured with and without a Si bonding layer. The microstructural evolution under three thermal cycling conditions was investigated, including thermal shock (air and water cooling) and burner rig tests. Results show that the thermal conductivity of RExAlyO/Yb2Si2O7 ranges from 0.798 W/(m.K) to 1.123 W/(m.K) from RT to 1400°C. The bondcoat Si significantly increases the thermal conductivity, reaching 2.335 W/(m.K). During the three thermal cycling processes, amorphous droplet crystallization occurred in the RExAlyO layer. The resulting volume shrinkage led to vertical cracks within the layer, which were blunted at the interface and did not penetrate through the coating. Under short-term hot-cold cycling (water-cooled thermal shock), the TGO growth rate was high. Under hot-cold cycling with/without a temperature gradient (burner rig tests/air-cooled thermal shock), the TGO growth rates were similar. The coatings exhibited excellent high-temperature stability.