Remy Mevrel

Microstructure of oxide scales formed on cyclically oxidized MCrAlY coatings

Abstract NiCrAlY coatings have been deposited by high rate triode sputtering on cast NiCrAl substrates. Cyclic oxidation tests were carried out at 1100°C on these NiCrAlY coatings with various yttrium contents for up to 1000 cycles of 1 h. The oxide scales were examined at different stages by scanning electron microscopy (equipped with energy-dispersive spectroscopy), by X-ray diffraction and, for some scales, by transmission electron microscopy. A variety of oxides (α-Al2O3, Y3Al5O12, YAlO3, Y4Al2O9, Y2O3, two spinels and NiO) were identified.

Simultaneous Determination of Residual Stresses in a Thin Alumina Layer Grown by Oxidation on a NiCoCralY Alloy and in This Alloy

With a proper choice of experimental conditions, we demonstrate that the sin2 ψ method can be applied to determine the residual stresses existing at room temperature in a thin alumina layer and in the subjacent zone of a nickel-base alloy on which it has grown. This method has been applied on a 5 pm thick alumina scale formed by oxidation in air, during 300 hours at 1100°C, on a NiCo21Cr24Al14Y.06 alloy. The residual stresses in the alumina layer are highly compressive and their magnitude corresponds to the calculated value of the thermal stresses, whereas the residual stress level in the metallic alloy remains low.