The Study Of Rare-earth Oxy-apatite-A Potential Material Of CMAS-resistance For Thermal Barrier Coatings

The typical 7 wt.%Y₂O₃-stabilized ZrO₂（7YSZ）,which possesses a suite of desirable mechanical and thermal properties,is widely used as a thermal barrier coatings（TBCs）material for many years.However,with the increasing engine service temperatures,coating degradation introduced by calcium-magnesium-alumino-silicate（CMAS）melts attack has emerged as a critical problem.Therefore,the sacrificial coating is deposited on the top of YSZ coating to mitigate the CMAS-attack.This type of coating will rapidly react with molten CMAS,and concurrently promote the reactive crystallization.The dense rare-earth oxy-apatite as the products can inhibit the penetration of the molten salts into TBCs and avoid the reaction of YSZ with CMAS melts effectively.The present study will investigate the CMAS-resistance and the chemical compatibility with YSZ of this new type of rare-earth oxy-apatite as a protective layer of YSZ.The results indicate that this new type of rare-earth oxy-apatite has superior molten silicate resistant capability and excellent chemical compatibility with YSZ.During the CMAS attack at 1300°C,the specimens developed a dense,continuous reprecipitated-diffused layer at RE-apatite/CMAS interface,without the formation of new phase.Meanwhile,in the system of apatite and YSZ,no new reaction products formed and some RE diffusion appeared after 24-h interaction at 1300°C.With the increase of the ionic radium,La-apatite has the thinnest reprecipitated-diffused layer,and the lowest concentration of RE diffusion to YSZ.Based on these results mentioned above,the rare earth oxy-apatite is prospective to be a potential impermeable out layer material against CMAS-attack.