Enhanced strength and ductility of pure copper at liquid nitrogen temperature

Abstract

An experimental study was conducted to investigate the improved ductility and strength of cold-rolled copper sheets. elucidate Its deformation mechanism at liquid nitrogen temperature (LNT) was elucidated. Tensile and bulging tests were conducted to comprehensively analyze the deformation behavior under uniaxial and complex stress states. The relationships between macroscopic deformation and microstructural evolution were quantitatively evaluated through scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM). At LNT, the ductility of pure Cu increased by 72.2% compared to room temperature (RT). The yield strength and tensile strength enhanced by 18.7% and 56.6%, respectively. The average limiting dome height (LDH) increased from 17.9 mm to 21.8 mm. These results indicated that pure Cu showed a synergistic enhancement of strength and ductility at LNT. Also, the work-hardening coefficient of pure Cu was found to be more dependent on temperature than on strain rate. In the biaxial stress state, the enhanced ductility at LNT was attributed to the reorientation of grains. Additionally, pure Cu exhibited an enhanced resistance to localized deformation. The increase in strength was due to a reduction in relative slip distance, but the significant increase in dislocation density, Peierls-Nabarro stress and strain hardening at LNT.