Oxidation behaviour of ultrafast slurry aluminized nickel

Abstract

The isothermal oxidation behaviour of ultrafast slurry aluminized pure nickel was studied between 900 and 1100 °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 Ni 2 Al 3 + NiAl coating. The oxidation curves exhibited a parabolic shape due to the formation of α-Al 2 O 3 scale. The parabolic rate constants increased from 950 to 1100 °C in line with the faster degradation of the coating. Moreover, the kinetic constant at 900 °C was higher than at 950 °C because of a greater formation of the less protective metastable θ-Al 2 O 3 scale developed rather than α-Al 2 O 3 . 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. • Ultrafast (35 min) slurry aluminizing of pure Ni leads to (Ni 2 Al 3 + NiAl) coatings. • On the ultrafast slurry coatings only Al 2 O 3 grow after air oxidation between 900 and 1100 °C. • The ultrafast slurry coatings have higher k p than pack-cemented coatings above 1000 °C. • Similar evolution of the microstructure of slurry and pack-cemented coatings upon oxidation