Microstructural and nuclear magnetic resonance studies of solid-state amorphization in Al-Ti-Si composites prepared by mechanical alloying

Three Al30Ti70-x Si-x (x = 10, 20, 30), along with an Al-rich (Al50Ti40Si10) and an Al-lean (Al10Ti60Si30) elemental powder blends were subjected to mechanical alloying by high-energy planetary ball milling to yield a composite microstructure with varying proportions of amorphous and nanocrystalline intermetallic phases. Microstructural characterization at different stages of milling was carried out by X-ray diffraction, high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Furthermore, Al-27 nuclear magnetic resonance (NMR) studies were undertaken to probe the mechanism of solid-state amorphization. Ball milling leads to alloying, nanocrystallization and partial solid-state amorphization followed/accompanied by strain-induced nucleation of nanocrystalline intermetallic phases from an amorphous solid solution. Both these amorphous and nano-intermetallic phases are associated with characteristic NMR peaks at lower frequencies (than that of pure Al). Thus, mechanical alloying of Al-Ti-Si appears a suitable technique for developing nanocrystalline intermetallic phase/compound dispersed amorphous matrix composites. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.