Cavity Nucleation and Growth in Nickel-Based Alloys during Creep

Abstract

The number of fossil fueled power plants in electricity generation is still rising, making improvements to their efficiency essential. The development of new materials to withstand the higher service temperatures and pressures of newer, more efficient power plants is greatly aided by physics-based models, which can simulate the microstructural processes leading to their eventual failure. In this work, such a model is developed from classical nucleation theory and diffusion driven growth from vacancy condensation. This model predicts the shape and distribution of cavities which nucleate almost exclusively at grain boundaries during high temperature creep. Cavity radii, number density and phase fraction are validated quantitively against specimens of nickel-based alloys (617 and 625) tested at 700 °C and stresses between 160 and 185 MPa. The model’s results agree well with the experimental results. However, they fail to represent the complex interlinking of cavities which occurs in tertiary creep.

Cavity nucleation in single-component homogeneous amorphous solids under negative pressure

“…Here, the parameter R is the reaction coordinate characterizing the cavity size. As a rule, the average radius of a cavity is taken as the reaction coordinate assuming that the cavity shape is close to spherical [11]. In this case, the basic equations of the classical theory of nucleation designed, for example, to calculate the free energy and the nucleation rate, can be adapted to the case of cavity nucleation without any significant changes [11].…”

“…As a rule, the average radius of a cavity is taken as the reaction coordinate assuming that the cavity shape is close to spherical [11]. In this case, the basic equations of the classical theory of nucleation designed, for example, to calculate the free energy and the nucleation rate, can be adapted to the case of cavity nucleation without any significant changes [11]. Nevertheless, the results of recent studies show that the classical nucleation theory can have limited applicability when the size and the distribution of cavities within the material are weakly dependent on its thermodynamic state [7,12,13].…”