Effects of air plasma spraying parameters on microstructure and bonding strength of GdPO4 thermal barrier coatings

Abstract

With the increase of the turbine inlet temperature of gas engines, the widely used Y2O3 partially stabilized ZrO2（YSZ）thermal barrier coatings (TBCs) have been unable to meet the requirements, and new generation TBCs that can survive ultra high-temperatures are urgently needed. Among many TBC candidates, GdPO4 has a great application prospect. In this study, GdPO4/YSZ TBCs were prepared by air plasma spraying, and the effects of preparation parameters, especially spraying power on the phase composition, surface morphology, microstructure and bond strength of GdPO4 coatings were investigated. The results show that the P loss takes place during spraying, and both GdPO4 and Gd3PO7 phases are detectable in the final topcoats, the content of the latter decreases by reducing the spraying power. The GdPO4 coating microstructure is mainly composed of piles of fully melted spray particles, among which there is porous micro-zone consisting of unmelted particles. With the decrease of the spraying power, the content of the micro-zone increases, and the coating thickness significantly decreases. The bonding strength of GdPO4/YSZ TBCs decreases with the decrease of spraying power, which is mainly because the cohesion of coating decreases with the increase of unmelted micro-zone. Therefore, low spraying power is not beneficial to the coating bonding strength.

Keywords

• thermal barrier coatings (tbcs)
• gdpo4
• air plasma spraying
• phase constitution
• microstructure
• bond strength