A crystalline interface separates two crystals (or grains) that are:
– of the same nature and structure: the interface is then referred to as a homophase interface or, more commonly, grain boundary; or
– with a different nature or structure: this is a heterophase interface.
Grain boundaries and heterophase interfaces play a major role in the behavior of performance materials that are most often used in polycrystalline form. In particular, they exercise a notorious effect on the mechanical properties of these materials: barriers to deformation; preferential regions for “intergranular” sliding during creep; sites of rupture under fatigue; etc. Basic knowledge of these interfaces seems
to be increasingly necessary with the development of materials whose grain sizes decrease until they reach the nanometric scale.
Much of the current understanding about interfaces comes from studying them using various microscopic and analytical methods. The micrographic images used in this chapter have been taken at different scales in consideration of the overall contribution of interfaces to a property of the material or their individual reaction to an interaction. Figure 2.1 shows an example of the image observed of one (or more) interface(s) depending on the method of observation.
Optic microscopy and scanning electron microscopy reveal only a trace of the interface on the free surface of the ...