Different pre-annealing and pre-oxidation treatments were conducted on a dual phase γ + β Ni-21Co-18Cr-22Al-0.2Y (at.%) bond coating for 1 hr at 1373 K (i) with or without a native oxide upon heating, (ii) in two different atmospheres upon heating, and (iii) under various oxygen partial pressures (pO 2 ) in the range of 0.1-10 5 Pa during oxidation. The chemical composition, structure, morphology and phase constitution of the resulting oxide layers were investigated using a range of analytical techniques. It is found that the exclusive formation of a continuous α-Al 2 O 3 layer without the simultaneous formation of NiAl 2 O 4 spinel was promoted for oxidation at low pO 2 . The formation of metastable θ-Al 2 O 3 was suppressed for a low fraction of the β phase, coupled with a high fraction of segregated Y at the initial bond coat surface. Initial Y segregation and incorporation of Y 2 O 3 and Y 3 Al 5 O 12 within the developing oxide layer was promoted in the absence of a native oxide and for heating in an inert atmosphere. The development of protrusions (i.e. pegs) at the oxide/coating interface, as a result of the incorporation of internal Y 2 O 3 precipitates by the inward growing oxide layer, was most pronounced upon heating in an inert atmosphere, followed by oxidation at an intermediate pO 2 .
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