The Contribution of Mechanical Spectroscopy to Understanding Grain Boundary Sliding

This review paper shows that grain boundary sliding (GBS) is a general phenomenon occurring in all classes of inorganic materials: ceramics, metals and composite materials. The occurrence of relaxations attributed to GBS is also quite general and therefore the mechanical spectroscopy constitutes a sensitive and universal technique to study such phenomenon. GBS is widely observed in ceramics. It can be due to the presence of an amorphous layer between the grains as in zirconia or to dislocations, as in alumina. In each case, a high temperature GBS peak has been identified. In metals, GBS is observed in some deformed materials but the correlation of such phenomenon with internal friction peaks has been controversial. In 1941, C. Zener describes a geometrical model of GBS that could give rise to a relaxation mechanism. In 1947, Ke observed a large relaxation peak in polycrystalline aluminum. This peak being absent in single crystals, the relaxation was attributed to GBS. Today, the Zener model can still be used in most cases for relaxations occurring in the grain boundaries. Instead, according to the grain boundary type, the material or the temperature, either dislocations or the gliding of a disordered layer produce the grain boundary relaxations.