ABSTRACT
Nickel-based superalloys are widely used as a gas turbine blade material and their integrity during service is important. When these alloys are creep deformed at high temperature, cuboidal shaped strengthening precipitates of 0 phase usually grow in the direction perpendicular to the loading axis [1-3]. In this chapter, a model for the mechanism of this rafting phenomenon is presented in terms of the free energies in narrow channels of the phase and the local equilibrium concentrations of the component elements. Anisotropic distribution of the free energy is attributed to the difference in stress state in the channels. The stresses caused by lattice misfit between the and 0
phases and dislocations formed at the =0 interface during the initial stage of creep deformation are then evaluated. Finally, the rate of rafting may be calculated from the difference in the local equilibrium concentration of component elements, and may be compared with experimental results.
