Degradation kinetics at 650 °C and lifetime prediction of Ni2Al3/Ni hybrid coating for protection against high temperature oxidation of creep resistant ferritic steels

The degradation kinetics of the Ni2Al3/Ni hybrid coating formed on creep resistant ferritic steel is studied by prolonged isothermal annealing experiments at 650 °C. The sequence of formation and subsequent consumption of all the intermediate phase layers are determined by intermittent analysis of the specimen at various annealing intervals. It is shown that the Ni5Al3 phase layer starts to form only when the outer Ni2Al3 phase layer is completely consumed and the growth kinetics of each of the intermediate layers differs from that of its subsequent consumption. A model is subsequently formulated to predict the lifetime of the coating studied.

► Phase transformation sequence in Ni2Al3/Ni coating on steel is identified at 650 °C.
► The Ni5Al3 layer forms only at a moment when the Ni2Al3 layer is totally consumed.
► Growth kinetics of an intermediate phase layer differs from its consumption kinetics.
► A model is proposed to predict the lifetime of the coating.