Suspension plasma sprayed yttria-stabilized zirconia coatings from a non-flammable solvent: A story of thermal cycling, erosion, and calcium-magnesium-alumino-silicate

Suspension plasma sprayed (SPS) yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) deposited from ethanol-based suspensions typically exhibit columnar microstructures that provide excellent strain tolerance and low thermal conductivity. However, the flammability of ethanol presents significant safety and scalability challenges, motivating the search for alternative non-flammable suspension media capable of producing comparable microstructural features and performance. For the first time, in this study, a non-flammable solvent based YSZ suspension was employed for the first time to deposit columnar SPS YSZ coatings, and their suitability as TBCs was studied through furnace cyclic testing (FCT), erosion, and calcium–magnesium–alumino–silicate (CMAS) infiltration experiments. The resulting coating microstructure exhibited a well-developed columnar morphology with discontinuous intercolumnar porosity, demonstrating a 97.4% longer thermal cyclic lifetime than previously reported water-based YSZ coating microstructure deposited by suspension high-velocity oxy-fuel spraying. In the non-flammable SPS coatings, failure during thermal cycling occurred predominantly by delamination at the thermally grown oxide (TGO)/top-coat interface, driven by TGO thickening and thermal expansion mismatch stresses. The erosion rate for the same coating was approximately seven times higher than that of previously reported ethanol-based SPS YSZ coatings because of its lower fracture toughness, with material removal dominated by crack propagation along interpass porosity bands. Compared with a water-based SPS YSZ coating, the non-flammable SPS coating microstructure exhibited a 45.3% reduction in CMAS infiltration, owing to its discontinuous intercolumnar pore network that restricted continuous penetration pathways. These findings demonstrate the potential of non-flammable suspensions as a novel and viable route for suspension-derived YSZ TBCs.