Preparation of the plasma-sprayed graded thermal barrier coating by co-injection of premixed powders through a single plasma torch

Abstract

ABSTRACTPlasma-sprayed partially stabilised zirconia (PSZ) coatings are being proposed for the molten salt environment at high temperature as they showed good corrosion resistance. In the present study, graded PSZ coatings were produced by the plasma spray technique by co-injection of premixed powders through a single plasma torch. A mixed phase structure, consisting of zirconia, mixed reaction phase of bond coat (BC) + zirconia and oxidised BC, was observed. Formation of the graded coating without reaction between zirconia and BC using a single plasma torch is an intricate process; therefore, optimisation of parameters was carried out. The cross-section SEM micrograph, Energy Dispersive X-Ray Analysis (EDX) line profile and elemental X-ray mapping of the optimised graded coating revealed that the graded coating was achieved without the reaction of BC and zirconia. Molten salt corrosion and thermal cycling studies were carried out on the duplex and optimised coating. The average adhesion strength of the graded coating improved marginally in comparison to that of the duplex coating.