Abstract
Results of structural studies performed with light microscopy and transmission electron microscopy on plasma sprayed NiCrAlY coatings isothermally exposed at 850 °C for 1, 10 and 100 hours are presented in this paper. The applied thermal treatment led to the decomposition of initial phases and to precipitation of α-Cr and γ'-Ni₃Al. It is shown that the precipitation of α-Cr in the γ/γ' matrix obeys orientation relationships.
Complete transformation of amorphous oxides into crystalline structures takes place within the 100 hour exposure. Spinel structures with spacings close to γ-Al₂O₃ are mostly formed, however, Cr₂O₃ and CrO₃ oxides were found too. No transformation to stable α-Al₂O₃ oxide has been observed.

Key words
NiCrAlY coatings, microstructure, thermal treatment, TEM studies

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