Oxidation Behaviour Of Ultrafast Slurry Aluminized Nickel

The isothermal oxidation behaviour of ultrafast slurry aluminized pure nickel was studied between 900 and 1100 degrees C in air for 100 h. The microstructure and composition of the coatings evolved with the increase of the oxidation temperature resulting in a progressive reduction of aluminium content of the initial bilayered Ni2Al3 + NiAl coating. The oxidation curves exhibited a parabolic shape due to the formation of alpha-Al2O3 scale. The parabolic rate constants increased from 950 to 1100 degrees C in line with the faster degradation of the coating. Moreover, the kinetic constant at 900 degrees C was higher than at 950 degrees C because of a greater formation of the less protective metastable theta-Al2O3 scale developed rather than alpha-Al2O3. While the oxidation kinetics of the ultrafast slurry coatings are one order of magnitude higher than that of pack-cemented coatings, the evolution of the microstructure is alike to the ones of slowly grown CVD-derived and slurry aluminide coatings.