الفهرس 
Chapter One: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Nanomaterials have grown as the basis of nanotechnology over the past few decades to have a profound impact on virtually all areas of materials research. Its unique features and characteristics are believed to revolutionize the world of science. There are two basic and complementary methods that have been developed to manufacture these materials. They are commonly referred to as ”bottom-up” and ”top-down” processes. Both are opposing in the sense that in the bottom-up approach, the nanoscale particles themselves are the building blocks of more complex nanostructures that are synthesized either by chemical or physical methods. Whereas the top-down method starts with bulk solids to obtain what is known as bulk nanostructured materials.
Among these ”top-down” methods, the most successful was severe plastic deformation. In recent years, severe plastic deformation (SPD) has emerged as an effective approach to producing ultrafine-grained structure (UFG) materials. Since then, extensive research has been conducted to develop SPD methods and techniques for fabricating several UFG metals and alloys.
Several SPD technology variants are now available that implicitly use this general feature of high hydrostatic pressure to fabricate a wide range of metals. The most advanced technique is equal channel angular pressure (ECAP), also known as equal channel angular extrusion (ECAE). Equal channel angular pressing techniques are one of the metal forming processes in which an ultra-large plastic strain is imposed on a bulk material in order to reach ultra-fine-grained and nanocrystalline metals and alloys.
The main aim of the current work is to investigate the effect of ECAP processing parameters, namely the number of passes, ECAP die angle, route type, and processing temperature, on the mechanical and electrical properties of pure Cu. In addition, the current study aims to provide a detailed mapping of the deformation behaviour of commercially pure Cu during ECAP as a function of increasing the imposed strain via accumulating the shear strain by increasing the number of processing passes using finite element method (FEM) simulation. The simulation findings were verified experimentally using the distribution of the Vicker’s hardness values. Finally, the interrelationships between the FE simulation, microstructural evolution, mechanical properties, and hardness distribution were presented. The response surface methodology (RSM) was used to identify the optimum ECAP processing parameters by analyzing the impact of ECAP conditions on responses.
A second-order regression model and analysis of variance were created to analyze the ECAP condition of optimum responses. A genetic algorithm (GA) was also applied to optimize the ECAP condition. Finally, a hybrid response surface methodology based on the genetic algorithm was created to improve the optimization of ECAP responses and their corresponding conditions evaluated using the genetic algorithm. The developed models were validated and compared with the experimental findings to prove that they are reliable as predictive tools.
The optimization findings revealed that route Bc was more effective in improving the hardness, yield stress, ductility, and impact energy, whereas route A was more effective in improving the ultimate tensile strength and the electrical conductivity of the Cu billets. Furthermore, the optimum die angle, number of passes, and processing temperature for the mechanical and electrical properties were also identified individually.