Grain boundaries are interfaces between crystallites of the same phase but different crystallographic orientation. They can be characterized as being low angle or high angle. This article discusses the measurements of grain-boundary energy with a brief summary of different schemes for measuring grain-boundary surface tension. The atomistic simulations of grain-boundary energy, measurement of grain-boundary migration and the techniques used to monitor grain-boundary migration are reviewed. Several considerations and effects influencing the computation of grain-boundary mobility are also discussed.

This article reviews network models and their applications for the simulation of various physical phenomena related to grain-boundary migration. It discusses the steps involved in the implementation of two and three-dimensional network models, namely, acquisition and discretization of the microstructure, formulation of the equation of motion, and implementation of the topological transformations. The article presents examples that illustrate the simulation of physical phenomena to demonstrate the predictive power and flexibility of network models.

This article provides a qualitative summary of the theory of diffusion bonding, as distinguished from the mechanisms of other solid-state welding processes. Diffusion bonding can be achieved for materials with adherent surface oxides, but the resultant interface strengths of these materials are considerably less than that measured for the parent material. The article describes three stages of diffusion bonding: microasperity deformation, diffusion-controlled mass transport, and interface migration. It concludes with information on diffusion bonding with interface aids.

Diffusion bonding is only one of many solid-state joining processes wherein joining is accomplished without the need for a liquid interface (brazing) or the creation of a cast product via melting and resolidification. This article offers a qualitative summary of the theory of diffusion bonding. It discusses factors that affect the relative difficulty of diffusion bonding oxide-bearing surfaces. These include surface roughness prior to welding, mechanical properties of the oxide, relative hardness of the metal and its oxide film, and prestraining or work hardening of the material. The article describes the mechanism of diffusion bonding in terms of microasperity deformation, diffusion-controlled mass transport, and interface migration. It concludes with a discussion on diffusion bonding with interface aids.