Synthesis of Al-Si-Ni Nanostructured Materials by Mechanical Alloying

An effort has been made to synthesize Al-based nanostructure by mechanical alloying (MA). Elemental powder of Al, Si and Ni were blended to obtain nominal composition of Al75Si15Ni10. Alloying was carried out in a high energy planetary ball mill using stainless steel grinding media at 300 r.p.m. up to 50 h. Toluene was used as the process control agent (PCA). The ball to powder weight ratio was maintained at 10:1. The phase evolution of the milled samples was studied by X-ray diffraction (XRD) analysis. The microstructural characterization of the milled powder was followed by scanning electron microscopy (SEM) and XRD. Dissolution of Si and Ni in Al was found to be 15% and 10% respectively along with the formation of some intermetallic phases. SEM micrographs showed that the powder morphology was changed from coarse layered structures obtained by very short period of milling to finer as the milling time increased. XRD and energy dispersive X-ray analysis (EDX) showed the formation of a homogeneous solid solution of the above said blends after milling for 50 h. The crystallite size, lattice strain (%) and lattice parameter were calculated from major XRD peaks. It shows that the crystal size decreased very rapidly up to 25 h of milling and then slowly became almost constant with further milling, whereas, lattice strain (%) increased gradually up to 25 h very rapidly and then very slowly became nearly constant with progress of milling. This suggests that major structural changes and dissolution of the alloying elements almost completed by 25 h, and further milling refined the product by MA. The lattice microstrain of the material increases exponentially. It increases rapidly up to 25 h and then increased slowly as the milling progresses further. The change of lattice parameter of Al-rich solid solution showed a rapid decrease throughout the process of MA. This is because of the entrance of Si and Ni atoms into the lattice of the Al which causes distortion in it. The change in the above mentioned parameters were determined up to 30 h of milling as on further milling Al peaks vanishes because of formation of partially amorphous structure along with some intermetallic phases