Mechanical behavior of ultrafine grained OFHC Cu at high strain rates

Abstract
The quasi-static and dynamic mechanical behaviors of ultrafine grained (UFG) oxygen free high conductivity copper (OFHC Cu) were compared with those of its coarse grained counterpart. A special focus was made on examining the effect of a UFG structure on the mechanical response under quasi-static and dynamic loading. For this purpose, OFHC Cu having the lamellar and equiaxed UFG structure was prepared by equal channel angular pressing of route A and B_c, respectively. The quasi-static and dynamic tests were conducted using a universal testing machine and the split Hopkins pressure bar tester in the strain rate range of 10⁻³ ~ 5000 s⁻¹. The UFG sample exhibited much enhanced yield stress over the coarse grained sample but showed a ductility loss due to the lack of strain hardenability under the quasi-static loading condition. In addition, shear failure occurred in the UFG samples even under quasi-static tensile mode. The deformation resistance of the equiaxed UFG sample against dynamic loading was found to be similar to that of the transverse lamellar UFG sample (i.e. impact loading perpendicular to the longitudinal lamellar direction), but that of the longitudinal lamellar UFG sample (i.e. impact loading parallel to the longitudinal lamellar direction) was inferior. In addition, the effect of ECAP pass number, which greatly affects the nature of the UFG structure, on the deformation resistance was briefly discussed.