YAG thermal barrier coatings deposited by suspension and solution precursor thermal spray
Tunji Adetayo Owoseni, Acacio Rincón Romero, Zdeněk Pala, Federico Venturi, Edward Lester, David M. Grant, Tanvir Hussain
Abstract
Yttrium aluminium garnet (YAG) is a promising topcoat material for thermal barrier coatings due to its high temperature stability and better CMAS (calcium-magnesium-alumino-silicate) resistance. YAG topcoats were deposited by suspension and solution precursor high-velocity oxy-fuel (HVOF) thermal spray. The relationships between processing, microstructure and final properties were studied through a range of characterization techniques and thermal cycling tests. The microstructure of the as-sprayed YAG topcoat from stoichiometric solution precursor (SP-YAG) had distributed pores and inter-splat boundaries, while the as-sprayed topcoat produced from suspension (S-YAG) had vertical and branched micro cracks, pores, and inter-splat boundaries. Both as-sprayed coatings were composed of amorphous phase, hexagonal yttrium aluminium perovskite (YAP) and cubic YAG. In thermal cycling tests, 20% of SP-YAG failure was reached after the 10th cycle; whereas, S-YAG reached the failure criteria between the 60th and 70th cycle. The failure of both the SP-YAG and the S-YAG topcoats occurred due to thermal stresses during the thermal cycling.