Multilayer GZ/YSZ thermal barrier coating from suspension and solution precursor thermal spray

Rare-earth (RE) zirconates, such as gadolinium zirconate (GZ), gained much attraction to be used for the next generation TBC. A double-layer and triple-layer TBC were deposited using the suspension and solution precursor high velocity oxy fuel (HVOF) thermal spray. A dense solution precursor GZ layer was intended to minimise the crack propagation from underneath, thereby inhibiting the CMAS infiltration. In the furnace cycling test, the double- and triple-layer coatings had a comparable cyclic lifetime. For the CMAS test, both the double- and triple-layer coatings were exposed to CMAS at 1250 °C for 30 mins. The CMAS deposits melted and infiltrated both coatings through the dense vertical cracks (DVCs). Interestingly, the GZ reacted with the molten CMAS to form a gadolinium apatite phase (Ca₂Gd₈(SiO₄)₆O₂) that was detected in the double- and triple-layer TBC. Both the double- and triple-layer TBCs succeeded in reacting with CMAS.