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.
Highlights
Thermal barrier coating (TBC) systems consist of a refractory topcoat and a metallic alloy bond coat to protect the superalloy substrates in gas turbines from high temperatures [1]
The combined plot of the thermogravimetric (TG) and the differen tial scanning calorimetry (DSC) plots of the solution precursor are shown in Fig. 1(a), where the upward direction indicates the evolution of exothermic effects
The nitrate vibration bands weaken as temperature increased; at 900 ◦C the spectrum shows the character istic vibrations of yttrium aluminium garnet (YAG), it shows the Al-O metal-oxygen vibration stretching bands at 788 cm− 1 and 688 cm− 1, while the Y-O vibration appears at the 722 cm− 1
Summary
Thermal barrier coating (TBC) systems consist of a refractory topcoat and a metallic alloy bond coat to protect the superalloy substrates (blades and vanes) in gas turbines from high temperatures [1]. The effectiveness of the TBC systems relies on the integrity of the topcoat specified by phase stability, thermal conductivity, low weight, high strain tolerance, coefficient of thermal expansion (CTE), resistance to ambient and high temperature corrosion and chemical compatibility with the underlying bond coat and the TGO—a protective oxide [2]. Yttria stabilized zirconia (YSZ) has been the standard material for TBC due to its low thermal conductivity, high melting point, high co efficient of thermal expansion and low density [1,3]. Electron beam physical vapour deposition (EB-PVD) deposited
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
