Plasma sprayed functionally graded thermal barrier coatings

Functionally graded thermal barrier coatings of the system yttria stabilise d zirconia/NiCoCrAlY were fabricated through plasma spraying using pre-allo yed composite powders as feedstock. Composite powders with different compos itions (75% NiCoCrAlY:25% YSZ; 50% NiCoCrAlY:50% YSZ and 25% NiCoCrAlY:75% YSZ) were prepared by mechanical alloying and plasma powder spheroidisation , and are subsequently sprayed successively in a single plasma torch to for m the functionally graded coating. This method has ensured a homogeneous co ating with satisfactory inter-layer formation, and a flexibility for deposi ting different numbers of inter-layers by changing the composition of the c omposite powders. In the present study, five-layered functionally graded co atings have been plasma sprayed. These coatings demonstrated attractive pro perties compared to the conventional duplex thermal barrier coatings. This is because of the unique microstructure formed in the functionally graded c oating with this new approach which also results in reduced residual therma l stresses in the coatings. (C) 1999 Elsevier Science B.V. All rights reser ved.