Mechanical behavior of plasma sprayed functionally graded YSZ/NiCoCrAlY composite coatings

Functionally graded Y₂O₃ stabilized ZrO₂ (YSZ)/NiCoCrAIY composite coatings were prepared using pre-alloyed and spheroidized composite powders. During the preparation of pre-alloyed powders and composite coatings, aluminum and chromium were oxidized and the so-formed metal oxides combined with zirconia forming unique mixtures of oxides. In this study, the mechanical properties of graded YSZ/NiCoCrAIY composite coatings, such as the elastic modulus, were investigated using a four-point bending test. The results showed that the elastic moduli and bending strength of individual layers of FGC decreased with an increase in the content of YSZ in the layer because of the increase in porosity of the coatings. The elastic moduli of the coatings also decreased with an increase in temperature. The elastic modulus for a five-layer functionally graded coating with a ceramic layer in tension during the bending test was lower than that of the coating with the ceramic layer in compression. This can be explained by the differences of the deformation behavior between the ceramic layer and metal layer during the four-point bending test. A laminated composite beam theory was used to explain these results.