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brief introduction of the historical background of grain boundary engineering for structural and functional polycrystalline materials is presented herewith. It has been emphasized that the accumulation of fundamental knowledge about the structure and properties of grain boundaries and interfaces has been extensively done by many researchers during the past one century. A new approach in terms of the concept of grain boundary and interface engineering is discussed for the design and development of high performance materials with desirable bulk properties. Recent advancements based on these concepts clearly demonstrate the high potential and general applicability of grain boundary engineering for various kinds of structural and functional materials. Future prospects of the grain boundary and interface engineering have been outlined, hoping that a new dimension will emerge pertaining to the discovery of new materials and the generation of a new property originating from the presence of grain boundaries and interfaces in advanced polycrystalline materials. [ABSTRACT FROM AUTHOR]

Extensive theoretical analysis and experimental observations show surface roughening transitions of crystals. The surface roughening is characterized by step free energy, which gradually decreases to 0 at the roughening transition temperature. For a crystal of finite size, the surface roughening transition is manifested by gradual increase of the curved edge and corner areas. In alloys, the interfaces between the solid and the liquid phases can be either singular, partially rough, or completely rough at different temperatures. Their thermally induced roughening transitions are similar to those of the solid-vapor interfaces. The interface roughening and the reverse transition to singular structures can also be induced by additives. The grain boundaries of any misorientation angles in oxides and metals also show roughening transitions. The singular grain boundaries have either flat, hill-and-valley, or kinked shapes, and with temperature increase or composition changes, they become defaceted to curved shapes. These defaceted grain boundaries are rough. It is thus possible to produce either singular or rough grain boundaries by heat-treatment or additives to vary their properties. [ABSTRACT FROM AUTHOR]

The two glass-ceramics studied here derive from the complex system (MgO,ZnO,Li2O)-Al2O3-SiO2 and are obtained by controlled devitrification of the same parent glass. Although they have the same chemical composition, one is a “β-quartz” (or “β-eucryptite”) type while the other one is a “β-spodumene” glass-ceramic. A detailed microstructural analysis of these materials has been performed at different scales by several complementary characterization methods (SEM, TEM, DTA, XRD and FTIR). This extensive study has shown the great microstructure difference (grain distribution, grain size, nature of vitreous and crystalline phases) between these two glass-ceramics obtained from the same parent glass. [ABSTRACT FROM AUTHOR]