Nanostructured materials in multicomponent alloy systems

Production of bulk nanostructured composites with amorphous matrix revealing a significant supercooled liquid region was carried out by die casting and mechanical alloying (MA) and subsequent consolidation at elevated temperatures. Multiphase materials with different volume fractions of nanocrystalline precipitates were prepared from as-cast fully amorphous samples by isothermal annealing. In contrast. MA powders were blended with insoluble metallic and oxide particles upon milling. The different samples were analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscope (SEM) and transmission electron microscopy (TEM), and viscosity measurements. The mechanical behavior of cast samples was investigated using constant (true) compression rate tests at strain rates ranging from 1 x 10(-5) to 3 x 10(-3) s(-1). The Newtonian viscous how behavior of the composites at temperatures around T-g is mainly triggered by the homogeneous how of the supercooled liquid. The easy flow behavior above T-g was used to consolidate bulk dense specimens from mechanically alloyed composite powders. Microhardness measurements at room temperature reveal a substantial increase of the hardness of the composites due to the uniform distribution of nanoscale particles. (C) 2001 Elsevier Science B.V. All rights reserved.