Improve forming properties by nanofabrication of tube microstructure using SPD technics
Abstract:
Nowadays, examining the mechanical properties of metals and improving them has been studied by many researchers. Severe Plastic Deformation (SPD) processes as scientific and attractive methods to create unique mechanical properties in metals by creating structures with very fine grains (UFG) in nanometer or several hundreds of nanometers (less than micron) has received much attention from researchers. Among the SPD processes, extrusion in channels of equal cross section (ECAP) is an effective method to produce materials with UFG structure to significantly improve their mechanical and physical properties. The aim of this study is to produce seamless copper tube from billet with improved mechanical properties, due to the reduction of its structure to nanometers or several hundred nanometers. Therefore, it has been tried to significantly reduce the grain size or crystal structure of copper samples. Therefore, pure commercial copper was subjected to severe plastic deformation by ECAP process during four stages at ambient temperature. For this purpose, an integrated ECAP mold with two channels perpendicular to each other and an external curvature of 37 degrees along with a mandrel was designed and built. Then, the samples produced at each stage of the ECAP process were subjected to direct extrusion to become seamless tube. The combined effect of extreme plastic deformation and direct extrusion of tube manufacturing on the microstructure, mechanical properties and electrical conductivity of copper tubes was studied. The results of examining the microstructure of the material by optical and scanning electron microscopes showed that the crystal structure of the copper samples deformed by the ECAP method and the tubes produced from them have changed significantly. The mechanical properties of tubes produced from ECAP samples in each pass (pass 1 to 4) have been measured by hardness and pressure tests at ambient temperature and their changes have been reported. In addition, the electrical conductivity of the produced samples was studied. Finally, the mechanical properties and electrical conductivity of copper produced by ECAP method and tubes produced by direct extrusion method were compared with each other. The obtained results showed that with the formation of very small grains (around several hundreds of nanometers) within the crystal structure of pure copper, the strength increased significantly, while its electrical conductivity decreased slightly due to the creation of very large grain boundaries. The comparison of the results obtained by the hardness and pressure test show that by applying the direct extrusion process and converting the samples produced by the ECAP method into seamless pipes, the strength, hardness and electrical conductivity increase a little. The comparison of the results obtained by the hardness and pressure test show that by applying the direct extrusion process and forming the samples produced by the ECAP method into seamless tubes, the strength, hardness and electrical conductivity increase a little.