Dynamic deformation and fracture behavior of ultra-fine-grained pure copper fabricated by equal channel angular pressing

Dynamic deformation and fracture behavior of ultra-fine-grained pure copper fabricated by equal channel angular pressing (ECAP) was investigated. The 1-pass ECAP'ed specimen consisted of fine dislocation cell structures, which were changed to very fine, equiaxed subgrains of 300-400 nm in size with increasing number of ECAP pass. The dynamic torsional test results indicated that maximum shear stress increased with increasing number of pass, but that the rate of the strength increase was higher in the 4-pass or 8-pass specimen than in the 1-pass specimen. This was because boundaries of subgrains formed during the 4-pass or 8-pass ECAP were more stabilized and high angled. Most of the ultra-fine-grained pure copper specimens were not fractured because adiabatic shear bands were hardly formed as the pure copper specimens were ductile and had high thermal conductivity, although a weak adiabatic shear band was observed in the 8-pass specimen. These findings suggested that the grain refinement by the ECAP was effective in strengthening of pure copper, and that the ECAP'ed pure copper could be used without much loss in fracture resistance under dynamic loading.