A phenomenological model for lifetime design of Ni _2Al _3/Ni hybrid coating formed on creep resistant ferritic steels

摘要

The phase layer transformation kinetics in the Ni _2Al _3/Ni hybrid coating formed on creep resistant steel P92 has been studied via a series of prolonged isothermal annealing experiments at 650 °C. All the intermediate phase layers of NiAl, Ni _5Al _3 and Ni _3Al formed in the coating by interdiffusion during isothermal annealing process. The phase layers of NiAl and Ni _3Al formed at the very beginning of isothermal annealing at the interface between Ni _2Al _3 and Ni, but the Ni _5Al _3 phase layer formed at the interface between the NiAl and Ni _3Al phase layer only at an annealing time at which the outer Ni _2Al _3 phase layer was completely consumed. The growth and consumption of the Ni _2Al _3 and NiAl phase layers and the growth of the Ni _3Al _5 phase layer were all parabolic, but the growth of the Ni _3Al phase layer obeyed the power rate law d = kt ~(1). The growth kinetics of an intermediate phase layer was found to be faster than the kinetics of its subsequent consumption. The rate constants in both the growth and consumption kinetics need to be determined for each of the intermediate phase layers at a particular temperature. The lifetime of the coating with an outer Ni _2Al _3 phase layer of any specified initial thickness and a sufficiently thick inner Ni layer can then be estimated using the lifetime design model delineated in this study.