Thermal Shock Analysis of Surface Al-modified 7YSZ Nano-thermal Barrier Coating

In order to improve the thermal shock resistance of 7YSZ nano-thermal barrier coating (TBC), bond coating NiCoCrAlYTa was prepared on simulated turbine blade by HVOF (high velocity oxygen flame). Subsequently, 7YSZ nano-ceramic coating was produced on bond coating as top coating. Al film was deposited on the surface of TBC samples. Then the Al-deposited TBCs were carried out by heat-treatment at different pressures (200, 250, 300 Pa). After that, the thermal shock tests of as-sprayed and Al-modified 7YSZ nano-TBC were taken from 1050 degrees C. to atmospheric water with holding time of 10 and 5 min, respectively. Micrograph and microstructure evolution of the TBC sample were characterized before and after thermal shock. The results show that a loose top layer with Al nano-grains is formed on the TBC surface due to evaporation and condensation of Al film at vacuum pressure. Besides, with increase of heat-treatment pressure, the density of loose layer is increased. A dense Al2O3 layer was in-situ synthesized under the loose layer due to the reaction of Al and ZrO2. The Al-modified 7YSZ nano-TBCs heat-treated at different pressures has less spallation area than the as-sprayed TBCs after withstood 73 thermal shocks, showing better thermal shock resistance.