In this study, four type of thermal barrier coating, two, three, five and seven composite layer with the same thickness (500 microns) was applied on the superalloy IN738 and the microstructure and properties are evaluated and compared. Coating was performed by plasma spraying process in air (AP). For more detailed comparison of the coating, other coating parameters are kept constant and the only variable was the number of layers. In this study, after the evaluation of the microstructure and chemical composition, the method of interface layer forming in conventional and new gradient coating was studied. The results showed that the microstructure, porosity and chemical composition of the multi-layer composite coatings, unlike the two-layer coatings, change gradually over near the intersection of thickness, so that by increasing the amount of NiCrAlY phase and the number of layers, porosity decreases to a large extent and improves the functional properties of thermal barrier coatings. In addition, fractography of fracture surface and microscopic examination was conducted on these coating systems. According to optical microscopy and Scanning electron microscopy (SEM), double-layers samples and 7-layers samples have the highest and lowest porosity percentage in the top coat, respectively.

کلمات کلیدی