In this paper, the microstructure and mechanical properties of three types of thermal barrier coating including: three, five and seven-layers composite, made of NiCrAlY / YSZ with the gradual change of chemical composition (FGM) and a conventional two-layers thermal barrier coating on the IN738 superalloy waere studied and compared. then, Coating by plasma spraying process in air (AP) was performed. For all coating systems, final thickness were considered similar (500 μm). In addition to more detailed comparison of the coating, the other parameters of coating are kept constant, the only variable was the number of layers. The wear test, microhardness, bending strength, SEM and optical microscopy analysis was performed on these four types of samples. Hardness tests indicated that the hardness of ceramic and metal layers increased by increasing the number of coatng layers and 1/5 times have been hard. The bending tests results showed that by increasing the number of layers, the strength and ductility of coating systems were increased. As a result, we can express that by increasing the number of layers, not only the coatings become more strength, but also become more flexible. The results confirmed that the gradient coating under conditions of high temperature are more corrosion resistance and greatly increases the lifetime of superalloys.

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