Microstructure of plasma sprayed NiCrAlY coating isothermally exposed at 850 degrees C for 1, 10 and 100 hours

Results of structural studies performed with light microscopy and transmiss ion electron microscopy on plasma sprayed NiCrAlY coatings isothermally exp osed at 850 degreesC for 1, 10 and 100 hours axe presented in this paper. T he applied thermal treatment led to the decomposition of initial phases and to precipitation of alpha -Cr and gamma'-Ni3Al. It is shown that the preci pitation of alpha -Cr in the gamma/gamma' matrix obeys orientation relation ships. Complete transformation of amorphous oxides into crystalline structures tak es place within the 100 hour exposure. Spinel structures with spacings clos e to gamma -Al2O3 are mostly formed, however, Cr2O3 and CrO3 oxides were fo und too. No transformation to stable alpha -Al2O3 oxide has been observed.