NANOSTRUCTURED MATERIALS SCIENTIFIC BACKGROUND AND TECHNOLOGICAL PERSPECTIVES

Nanostructured materials represent a special state of solid matter that consists primarily of incoherent interfaces (grain or interphase boundaries) formed between nanometer-sized crystallites of different crystallographic orientations. The atomic arrangement in the incoherent interfaces is characterized by a reduced density and nearest neighbor coordination number relative to the glassy or crystalline state. The reduced density and coordination is due to the misfit between the crystallites of different crystallographic orientations that are joined together at the interfaces. The reduced density and nearest neighbor coordination number leads to a new type of atomic structure which exhibits properties that differ (sometimes by many orders of magnitude) from the ones of crystals and glasses with the same chemical composition. Nanostructured alloys permit the alloying of components that are immiscible in the crystalline and/or glassy state. Solids formed by assembling nanometer-sized glassy sphere seem to open the way to generate a new type of glasses, called nanoglasses. Although discovered less than 15 years ago, nanostructured materials have started to enter the regime of technological applications. A few examples (hard, wear resistent nanostructured materials, soft magnetic nanostructured substances, near net shape forming of nanostructured ceramics and magnetic cooling) are presented.