Effect of Constrained Studded Pressing on the Microstructure and Residual Stresses for Producing Nanostructure Pure Copper Sheet

Severe plastic deformation (SPD) have been established to produce ultrafine-grained and nanostructure materials. One of the newly introduced methods is the constrained studded pressing (CSP) technique. A limitation of the CSP process is the creation of surface cracks. The most essential factors affecting surface cracks are residual stresses. In the current research, residual stresses distribution was studied on copper sheet under CSP using the finite element method. In addition, for laboratory study, microstructure and residual stress evaluation were studied before and after applying the CSP method. The microstructures of the annealed and deformed copper sheets have been observing by an optical microscope. The grain size, dislocation density, and the residual stresses were tested using an X-ray diffraction. The average grain size decreased from ۲۷ μm in the annealed sample to ۱۱ μm in the first pass sample. In the ۱۰th pass, the average grain size decreased to ۷۵۰ nm. The smallest reduction in grain size was achieved after applying the first pass, but with the increase of the applied strain in the final pass, the highest dislocation density was created in the microstructure. Therefore, by increasing the density of dislocations and followed by dynamic recovery, it caused the largest decrease in grain size compared to other samples. The residual stresses were altered from +۱۵۳.۲ MPa for the annealed sample to -۴۸.۶ MPa in the ۱۰th pass sample. According to this research, the application of more strains is directly related to the creation of compressive residual stresses and grain refinement.

Keywords:

Constrained studded pressing , Copper sheet , Microstructure , Residual Stress , Severe plastic deformation