Integration of mechanical alloying and equal channel angular extrusion for production of nanostructured materials

The main objective of this study is to develop the technology to produce nanostructured materials with superior mechanical and chemical behavior. The focus of this research is mainly on two issues: (1) Use of mechanical alloying (MA) to produce nanostructured titanium silicide (Ti5Si 3) in powder form. (2) Use of equal channel angular extrusion (ECAE) for consolidation of mechanically alloyed powder in bulk form by preserving the fine scale structure.; Nanostructured materials are a special group of materials with grain size less than 100 nanometers (nm), with a high percentage of atoms located at their grain boundaries. Due to the special structural arrangement of atoms, nanostructured materials are capable of developing much higher strength and stronger resistance to chemical attack, as compared to materials with conventional structure (grain size ranging from micrometers to millimeters). Because of their extraordinary mechanical and chemical properties, nanostructured materials have attracted a lot of attention in industry today. However, progress made to date in the production of these materials is limited to laboratory quantities and thin layers for surface coatings. In order that engineered nanostructured materials exhibit such superior properties, the essential requirement is that these materials should be in the bulk-processed condition and in larger quantities, suitable for industrial applications. This research achieves this by integrating the mechanical alloying process for production of nanostructured powders, and equal channel angular extrusion process to consolidate these powders and preserve their fine structure in bulk form.; MA is a high-energy ball milling process used to produce nanocrystalline and amorphous materials in powder form. The design of experiments statistical method (23 factorial design) is applied to optimize this process to produce nanostructured titanium silicide (Ti5Si3) in powder form. ECAE is a process that produces intense and uniform plastic deformation caused by simple shear of the material. This process has proven to be an effective method for forming nanocrystalline materials in bulk form. A 4 x 2factorial design was used to optimize the ECAE process. Finite element analysis and other modeling studies are presented to support the experimental work performed. X-ray diffraction (XRD) was used to determine the grain size of the material in powder form and the final product. Vickers method is used to measure the microhardness.; The main interest was on the production of nanostructured titanium silicide, a material with many applications in aerospace, transportation, oil industry etc. The titanium silicide material in powder form with grain size of 1 mum (micrometer) was subjected to a mechanical alloying process, which resulted in a nanostructured powder with a grain size of less than nm. To avoid the high temperature involvement used in traditional powder consolidation methods, which in turn causes the coarsening of grains, the nanostructured powder was consolidated using the ECAE process. The final product possessed a Vickers microhardness as high as 1500, and a grain size of less than 10 nm.