Synthesis of nanocomposites by mechanical alloying

Nanocomposites were synthesized by the solid-state powder processing technique of mechanical alloying in Al–Al₂O₃, TiAl–Ti₅Si₃, and MoSi₂–Si₃N₄ systems. The mechanically alloyed powders were consolidated to full density by techniques such as vacuum hot pressing, hot isostatic pressing, and combinations of them. The as-milled powders as well as the consolidated compacts were characterized for their crystal structure features using X-ray diffraction and for the microstructural features using scanning and transmission electron microscopy techniques. Mechanical properties such as hardness, ductility, and fracture toughness were also measured. It has been shown that it is possible to produce a high volume fraction of the reinforcement of nanometer dimensions and that the properties of the nanocomposites are significantly better than those of the monolithic materials. Superplastic deformation has been demonstrated in TiAl–Ti₅Si₃ composite even when 60 vol.% of the ceramic reinforcement was present.