IMECE2002-33728 PREPARATION OF NANOCRYSTALLINE TITANIUM SILICIDE POWDER AND ITS CONSOLIDATION USING SODIUM SILICATE

ABSTRACT Statistical design of experiments was employed to assess the effect of mechanical alloying variables and the chemical binder (sodium silicate) percentage on the crystallite size of mechanical alloyed titanium silicide powder and the microhardness of samples consolidated by chemical bonding. The results indicate that mechanical alloying the powder with higher milling time, higher milling speed and lower ball-topowder ratio and consolidating with 20% sodium silicate gives a combination of fine crystallite size and good microhardness in the compact. INTRODUCTION Nanostructured materials have a significant fraction of the total atoms at their grain boundaries [1], as their structure falls in between those of polycrystalline materials and amorphous materials. In polycrystalline materials most atoms are present within the grains and the grain boundaries consist of relatively few atoms. In contrast, amorphous materials do not have grains or boundaries. For this reason, the behavior of nanocrystalline materials is quite different from the behavior of conventional polycrystalline materials or amorphous materials. Of particular interest to mechanical engineers is the fact that nanostructured materials tend to have much greater hardness than conventional polycrystalline materials and also possess considerable high temperature ductility. While the techniques for producing nanostructured materials as thin films have been relatively well established [2], those for making bulky nanostructured products have received relatively little attention. Conventional sintering of a nanostructured powder would lead to significant grain coarsening and reversal to polycrystalline form. Attention therefore should be paid to the preservation of the nanostructure after consolidation into bulk. Some successful attempts have been made in this direction by employing self-propagating high temperature synthesis (SHS