Corrosion kinetics of a directionally solidified Ni-base superalloy

A variety of experiments were carried out to characterize the corrosion kinetics of a longitudinally oriented directionally solidified Ni-base superalloy, DS GTD-111, commonly applied as a first- and second-stage blading material in electric power generation gas-powered turbines. Under operating environments, the airfoil sections of turbine blades sustain surface-initiated damage due to the superimposed centrifugal stresses, elevated temperature and presence of corrosive reactants in the environment. As a consequence, surface cracking curtails the service lives of such components. To thoroughly characterize the stress-free and stress-assisted kinetics of diffusion and cyclic oxide rupture, several types of experiments are conducted: low cycle fatigue, thermomechanical fatigue, and thermogravimetric analysis, among others. A key goal of this study is to provide data necessary for the development of diffusion kinetics models. Accordingly, the study is divided into two parts: stress-free diffusion and stress-assisted rupture. Models are developed for each of these conditions.