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Document 2002-158

Studies on Nanostructured Titanium Silicide

M.N. Srinivasan and V. Mandakolathur Department of Mechanical Engineering Lamar University, Beaumont, Texas 77710

Introduction: Nanostructured materials have a significant fraction of the total atoms at their grain boundaries1, 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 established2, 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) 3 but there is need for investigating alternative routes for consolidation that ensure preservation of the nanostructure. The first author is the leader of several investigations looking into the possibility of employing the Equal Channel Angular Extrusion (ECAE) process for this purpose. It has already been demonstrated that nanostructured tungsten carbide billets can be successfully produced by subjecting mechanical alloyed (nanostructured) powder to ECAE 4. In the present paper, the results of using this combination for producing titanium disilicide billets will be presented and discussed.

Silicides and silicide matrix composites involving titanium and molybdenum are considered as advanced high temperature materials. From the mechanical engineer’s viewpoint, synthesis of nanostructured forms of these silicides would pave way for further improvement in the high temperature behavior as the hardness and the high temperature ductility of the nanostructured forms are much greater. With this in view, the present authors conducted an investigation involving the consolidation of nanostructured titanium disilicide powder. The powder was first mechanical alloyed (MA) to a fine size using an attritor, which is a high-energy ball mill. The fine powder was then consolidated using ECAE.

Mechanical Alloying: This process was originally developed by Benjamin 5 for producing oxide dispersion strengthened superalloys, but has since been used by many investigators to produce fine-scale powder. The attritor is popular equipment for mechanical alloying and consists of a vertical shaft with radial arms rotating in a chamber. The material to be milled is placed in the chamber along with the grinding balls made of hard materials. The milling is usually performed in an inert atmosphere.

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Mandakolathur, V., & Srinivasan, M. (2002, June), Studies On Nanostructured Titanium Silicide Paper presented at 2002 Annual Conference, Montreal, Canada. 10.18260/1-2--10388