Boundary mobility

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... 

Fig. 9 Dependence of grain boundary mobility on total impurity content in pure Al. 

Solute atoms do not always reduce grain boundary mobility. Small amounts of Ga in AI will enhance grain boundary migration. 

Equation 13.7 shows that the velocity is proportional to the pressure through a boundary mobility, MB, itself proportional to the self-diffusivity, D. The activation energy for boundary motion will therefore be that for crystal self-diffusion as expected for a crystal diffusion-limited process. 

Observations of further solute-atom drag effects have been reviewed [2, 13], A number of effects measured as a function of driving pressure, temperature, and solute concentration appear to follow the general trends indicated in Fig. 13.6. The approximate nature of the model makes some discrepancies unsurprising. In Fig. 13.9, the discontinuous increases in boundary mobility as the temperature is increased are presumably caused by successive detachments of portions of a solute-atom atmosphere that exerted a drag on the boundaries. 

M.F. Ashby. The influence of particles on boundary mobility. In N. Hansen, A.R. Jones, and T. Leffers, editors, Recrystallization and Grain Growth of Multi-Phase and Particle Containing Materials, pages 325-336, Roskilde, Denmark, 1980. Riso National Laboratory. 

K.T. Aust and J. W. Rutter. Effect of grain boundary mobility and energy on preferred orientation in annealed high purity lead. Trans. AIME, 224 111-115, 1962. 

Ni-20Cr 0 0.35 RE addition results in reduction in free S O content, increase in interfacial energy and grain boundary mobility, low cavitation [33]... 

Rg is the radius of curvature of the grain, and Mg/, is the grain-boundary mobility. 

The occurrence of attachment or separation depends on the mobility of the pores and boundaries. For a pure, single-phase material, the boundary mobility Mb is controlled by atom diffusion across the boundary ... 

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