Interfaces

Abstract

We can define an interface between any two phases, say fiber and matrix, as a bounding surface where a discontinuity of some kind occurs. The discontinuity may be sharp or gradual. In general, the interface is an essentially bidimensional region through which material parameters, such as concentration of an element, crystal structure, atomic registry, elastic modulus, density, and coefficient of thermal expansion, change from one side to another. Clearly, a given interface may involve one or more of these items. Most of the physical, chemical, or mechanical discontinuities listed are self-explanatory. The concept of atomic registry perhaps needs some further elaboration. In terms of the atomic registry types, we can have a coherent, semicoherent, or incoherent interface. A coherent interfaces is one where atoms at the interface form part of both the crystal lattices; that is, there exists a one-to-one correspondence between atomic sites on the two sides of the interface. In general, a perfect atomic registry does not occur between unconstrained crystals. Rather, coherency at the interface invariably involves an elastic deformation of the crystals. A coherent interface, however, has a lower energy than an incoherent one. A classic example of coherent interface is the interface between G-P zones and the aluminum matrix.