Heat-treated lanthanum magnesium hexaaluminate coatings exposed to molten calcium-magnesium-alumino-silicate

摘要

LaMgAl11O19 (LMA) coatings usually have a large amount of amorphous phase due to the rapid cooling during spraying, which will not benefit the service lifetime in aeroengine. Fortunately, the thermal cycling lifetime of LMA TBCs can be improved by heat treatment. Moreover, the hot corrosion degradation with calcium-magnesium-alumino-silicate (CMAS) attracts much attention recently. Therefore, to clarify the influence of heat treatment on CMAS corrosion behaviour, plasma-sprayed LMA coatings were isothermally heat-treated and then exposed to CMAS. Results indicate that heat treatment promoted a crystallization of LMA coatings, but the molten CMAS had completely penetrated into LMA coatings along the increased and widened vertical micro cracks. It is the isotropic pores that determine the penetration kinetics of CMAS to LMA. CaAl2Si2O8 and MgAl2O4 were the predominant reaction products in the superficial layer, while Ca3La6(SiO4)(6) interpenetrated with the residual LMA in the inner layer, forming a corroded bilayer for LMA coatings.