High Strain Rate Deformation Of Ultra-fine-grained Pure Copper

Ultra-fine-grained pure copper fabricated by equal channel angular pressing (ECAP) has been widely investigated because of its excellent mechanical properties, but the mechanical properties and microstructure of ultra-fine-grained pure copper deformed at high strain rate has ben rarely investigated, and most of the materials was deformed at a certain strain rate and temperature in practice, so the study of dynamic mechanical properties of UFG pure copper deformed at different conditions is of great important significance. So in this present work, the UFG8p pure copper fabricated by ECAP will under dynamic impact by SHPB, the strain rate is1500s-1, deformation temperature is425K,373K,298K,233K and173K, the samples of UFG4p pure copper and CG pure copper were coMPared to UFG8p pure copper. Then transmission electron microscopy (TEM) and XRD were used to analysis the changes of microstructure as well as micro-strain, dislocation density and twin density of the samples that deformed at different conditions. The investigation indicated that the grain size and dislocation density will be saturate after conventionally extruded8passes by ECAP, the strength of the materials will not raise but decrease if continue to extruded. The strength of the UFGgp pure copper will be increased at high strain rate, use this principle the samples that deformed by ECAP and SHPB were conducted to tensile test and then analysis of the change of mechanical properties of these samples.The results of dynamic mechanical properties indicated that flow stress of ultra-fine-grained pure copper was increased with decreasing deformation temperature, UFGgp+SHPB (173K) pure copper has the highest flow stress581MPa. Comared with CG pure copper the strain hardening ability of UFG pure copper is very poor and the strain hardening effect was increased with decreasing deformation temperature. The results of TEM indicated that deformation twin clusters were exist in the ultra-fine-grained pure coppers that were conducted to SHPB at different temperatures and dynamic recrystallization occurs in UFG4P+SHPB (298K) pure copper and UFG8p+SHPB (425K) pure copper. Microstructure results indicated that the grain size of UFGgp pure copper was refined from92um to390nm and it can be further refined by SHPB, the grain size of UFG8p+SHPB (173K) pure copper further refined to300nm or so which is obviously lower than that of UFG8p pure copper. UFG8p+SHPB (425K) pure copper a minimum of grain size230nm which is due to dynamic recrystallization refinement. The results of XRD show that the micro-strain and dislocation density of UFG8p pure copper was increases further after SHPB impact at room temperature and low temperature, but the micro-strain and dislocation density of UFGsp+SHPB (425K) pure copper is lower than UFG8p pure copper which is due to dynamic recovery effect at high temperature. The twin density of ultra-fine-grained pure copper was increase with decreasing deformation temperature. The results of tensile test indicated that the yield strength and tensile strength of samples that are conducted to ECAP and SHPB, and the yield strength of UFG8p+SHPB pure copper was increase with decreasing deformation temperature. The elongation of UFG8p+SHPB pure copper was decreasea with decreasing deformation temperature, but the change is not obvivous.