Grain boundary driving force

The second, the grain boundary driving force, Ky, is given by... 

If there are a number of inclusions at the boundary, the boundary driving force may be insufficient to move it past the inclusions. The grain size limit in this case is ... 

In reality, below 550°C the driving force becomes so large that it cannot be contained and the iron transforms from f.c.c. to b.c.c. by the displaeive mechanism. Small lens-shaped grains of b.c.c. nucleate at f.c.c. grain boundaries and move across the... 

The physical process of melt ascent during two-phase flow models is typically based on the separation of melt and solid described by Darcy s Law modified for a buoyancy driving force. The melt velocity depends on the permeability and pressure gradients but the actual microscopic distribution of the melt (on grain boundaries or in veins) is left unspecified. The creation of disequilibria only requires movement of the fluid relative to the solid. 

During the experiment the boundary displacement is recorded. Its derivative with regard to time is the velocity v of grain boundary motion, which is related to the driving force p by the boundary mobility m = v p. For convenience we use the reduced boundary mobility... 

The driving forces necessary to induce macroscopic fluxes were introduced in Chapter 3 and their connection to microscopic random walks and activated processes was discussed in Chapter 7. However, for diffusion to occur, it is necessary that kinetic mechanisms be available to permit atomic transitions between adjacent locations. These mechanisms are material-dependent. In this chapter, diffusion mechanisms in metallic and ionic crystals are addressed. In crystals that are free of line and planar defects, diffusion mechanisms often involve a point defect, which may be charged in the case of ionic crystals and will interact with electric fields. Additional diffusion mechanisms that occur in crystals with dislocations, free surfaces, and grain boundaries are treated in Chapter 9. 

Fig. 24. Driving force for an amorphous grain boundary phase in equilibrium with /tes as a function of composition in the system Si-N-O-Al and strength of interaction [330]...

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