Evaluation of three kinds of MCrAlY coatings produced by electrospark deposition

Three kinds of MCrAlY coatings with different aluminum contents (5%, 8%, 12%) were prepared by electrospark deposition (ESD), their microstructure and oxidation behavior were studied by SEM and XRD. The results showed that the phase composition of the coatings changed from single gamma-Ni to gamma-Ni+beta-NiAl hypoeutectic to gamma-Ni+beta-NiAl hypereutectic with increasing aluminum content, and their solidification morphologies changed from cluster of cellular structure to cellular dendrites to coarse dendrites with secondary arms. When exposed at 1000 degrees C, the coatings with higher Al content had a stronger tendency to form theta-Al2O3 in the initial several hours. After 100 h of oxidation, a dense and adherent alpha-Al2O3 scale formed on all of the three coatings but the thickness of alpha-Al2O3 scale and the amount of remaining theta-Al2O3 increased with increasing Al content. These results revealed different characteristics of ESD MCrAlY coatings which could provide scientific guidance for industrial application.