Grain boundary velocity

During discontinuous grain growth, the grain boundaiy can move as is shown in Figure 16.14 [37]. Here we see that the grain boundary velocity is perpendicular to the grain boundary and in the direction... 

Schematic of abnormal grain growth showing the grain boundary veloc-...

In solution drag, the width of the grain bovmdaiy, w, is the zone over which impurities interact. The grain boimdary thickness is taken to be independent of grain size. The diffusion coefficients of the host, D , and the impvirity, D/, will depend on the structure in the grain boundary. Impurities can therefore have an effect on the grain boundary velocity, Vg, by either their effect on the Co term or an effect on the diffusion coefficients for host and impurity. 

When pores are the second phase, they are mobile and move at a velocity equal to the velocity of the grain boundary, thus Vgi, = Vp = MpFp, where the pore mobility, Mp, and the drag force on the pore, Fp, is given in Table 16.8. Separation of the pores from the grain boundaiy occurs when Vgi, > Vp [85]. Thus the pores exhibit a drag on the grain boundary velocity, giving [86]... 

AVhat is the maximum grain boundary velocity before the 0.13 fim diameter pores will detach from its grain boundary shown in Figures 16 and 17. in the sintering of pure AI2O3 at 1550°C. Assume that surface diffusion is responsible for the grain boundary movements. 

To model the process, one needs to obtain a relationship between the grain boundary velocity Wgb and the driving force acting on the boundary. And since the situation is almost identical to that encountered during the growth of a solid/liquid interface (Fig. 9.3), Eq. (9.14) is directly applicable and... 

If the instantaneous rate of grain growth is used to represent the average rate of grain-boundary migration Vb, also known as grain-boundary velocity, there is... 

Figure 7.2. Driving force for grain boundary migration versus grain boundary velocity. ...

Explain the variation of solute segregation at grain boundaries with increasing temperature. Draw schematically and explain the variation in grain boundary velocity with temperature for pure, slightly impure and highly impure materials. 

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