Interface structure and growth

The structure of an interface has a strong say in its growth rate. In general, the low energy, coherent and semi-coherent boundaries have low mobility; the high energy, incoherent boundaries have high mobilities. So, if a precipitate (say, of phase) shares a coherent (or semi-coherent) boundary and an incoherent boundary with two different grains (say, of $\alpha$ phase) as shown in Fig. 25, then, in general, the incoherent interface will grow at a faster velocity than the coherent interface (as indicated). Such differences in the growth rates of different interfaces of a precipitate can result in interesting precipitate morphologies; the Widmansttten morphology is in fact, a result of such differing growth rates of different parts of the precipitate-matrix interface.

Figure 25: The interface structure and growth; in general, coherent boundaries have low mobility and incoherent ones have high mobilities.

[scale=0.4]Figures/InterfaceStrGro.pdf