Rare-Earth Oxides Blended With Yttria-Stabilized Zirconia Thermal Barrier Coatings for Improved Resistance to Sand Adherence and Calcia-Magnesia-Alumino-Silicate (CMAS) Infiltration

Military rotorcraft are particularly susceptible to engine damage from environmental particulates. While inertial particle separators are efficient at removing large particles, fine particulates (75 μm or smaller) are still entering the engine. Once into the hot-section, these fine particulates melt, impinge the hot-section components, and solidify as calcia-magnesia-alumina-silicate (CMAS) glasses. Infiltration from these glassy deposits can significantly reduce component lifetimes through the loss of strain tolerance and increased thermal conductivity within the thermal barrier coatings (TBCs) protecting the underlying substrates. Engine life knockdowns can lead to significant increases in the operations and sustainment costs of military aviation assets. In addition, the adhesion and build-up of the glassy CMAS deposit on hot-section components can lead to rapid performance degradation, which has resulted in the loss of aircraft and loss of life incidents during military operations in particle-laden environments. The Army Research Laboratory (ARL) is working to develop sandphobic coatings that are resistance to molten sand adhesion and the buildup of glassy CMAS deposits. To this end, this paper/presentation will focus on recent results from blending rare-earth oxides (REO) with yttria-stabilized zirconia thermal barrier coatings. Gadolinia powder was mixed with eight (8) weight percent yttria-stabilized zirconia (8YSZ) powder for consolidation via air plasma spray onto Inconel 718 discs (1-in diameter) and tested in the Hot Particulate Ingestion Rig (HPIR) under engine-relevant conditions, using AFRL-02 synthetic sand. The as-processed and tested samples were characterized using optical microscopy (OM) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). Preliminary results show that mixing REOs with 8YSZ can significantly reduce molten sand adhesion compared to pure 8YSZ.