Defect Interactions and the Complexity of Real Material Behavior

1 Defect Interactions and the Complexity of Real Material Behavior 

We begin our discussion with the consideration of diffusion. In earlier chapters, we noted that diffusion is mediated by the presence of point defects. However, until now, we have not given any quantitative analysis of the lubricating effect of other defects in the context of diffusion. We have already seen in fig. 9.1 that bulk diffusion can be negligible in comparison with the diffusion that takes place along surfaces, grain boundaries and dislocations. As a particular realization of this class of problem, we consider the case of surface diffusion with special reference to some of the counterintuitive diffusion mechanisms that take place at surfaces. 

A second fundamental theme that will be taken up in this chapter in which there is an interplay between the various types of defects introduced earlier is that of mass transport assisted deformation. Our discussion will build on the analysis of diffusion at extended defects. We will begin with an examination of the phenomenology of creep. 

A third example in which there is a mutual interplay between the different types of defects that we have discussed in previous chapters is that provided by the 

The next example that will be set forth as an example of a problem in which multiple defect types can be present simultaneously is that of fracture. Our discussion will begin with an examination of the way in which cracks can be built up as superpositions of dislocations. This leads naturally to questions of the interaction of dislocations and cracks and culminates in the analysis of the intriguing problem of crack tip nucleation of dislocations. 

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