The influence of an ECAP-based deformation process on the microstructure and properties of electrolytic tough pitch copper

Abstract

Samples of electrolytic tough pitch copper were deformed in equal channel angular pressing with enhanced productivity to quickly refine its initial coarsegrained microstructure at room temperature. The evolution in microstructure and changes in a broad range of properties were compared to a sample in the undeformed state. The microstructure evolution was evaluated using electron backscatter diffraction for both states and transmission electron microscopy for a detailed microstructure characterization of the deformed sample. The microstructure observations were correlated with the results of tensile tests, electrochemical tests in 3.5 wt% NaCl, electrical conductivity measurements and thermal stability up to 200°C. The ECAP process employed in this study caused a grain refinement from about 16 µm to about 600 nm. The microstructure refinement caused a 50% increase in both the YS and UTS. The elongation to failure, due to the high amount of LAGBs, maintained a high value of 13.3%. The corrosion and pitting potentials were higher for the deformed sample. Furthermore, the grain refinement caused a decrease in electrical conductivity from 100.2% IACS to 93.1% IACS, a drop of 7% IACS. The deformed sample displayed thermal stability up to a temperature of 175°C, where there was a drop in micro-hardness of more than 10%.

The Influence of A Cross-Channel Extrusion Process on The Microstructure and Properties of Copper

“…The distinct differences in the mechanical strength were caused by the grain boundaries and dislocation strengthening mechanisms. Similar results were reported for the tensile tests that were performed on the sample that was extruded by CCE once [66], where the UTS was approximately 400 MPa and the total elongation was approximately 13% after extruding six times by ECAP with two turns (route B C ); similar results were also described in [70] for samples receiving 10 passes of ECAP (B C ). Additionally, after ARB was performed four times [24], the UTS values were similar, while the average grain size was approximately 200 nm, which is significantly lower than the grain size that was obtained in the present study.…”

“…The abovementioned results are in contrast with the literature data, where grain refinement by mtECAP [66] caused a 7% increase in copper’s resistivity, which is similar to the results that were shown by [29,62] and was explained by the electron scattering caused by the structural defects. The increase in the electrical resistivity that is caused by grain refinement is not significant and, for pure copper, is on average 2–4%.…”

“…The fatigue fracture of the samples after ECAP strongly differs from the surface relief of the samples in the coarse-grained state and the deformation parameters, and other authors have reported similar copper behaviors that are associated with the plastic breakthrough that occurs with an increase in the deformation [62,66] or the reduction in the number of dimples and created cleavage planes, which indicated the existence of a mixed ductile-brittle fracture type, as has been demonstrated by the tensile ductility reduction [71].…”

Solid-state welding of ultrafine grained copper rods

“…During processing, after exceeding a specific accumulative strain, the mechanical property values saturate, and further passes only result in fluctuations of the properties by a few percent. After 8 passes, the tensile strength, depending on the type of copper (99.98% pure [19], commercial purity level 99.90% [22] and electrolytic tough pitch (ETP) [23]) increases by at least 60% in comparison with the coarse-grained material. Subsequent operations may cause a slight decrease in the mechanical properties of 90.77% [24] and 99.44% [25] UFG pure copper, as further processing no longer causes a noticeable drop in grain size [19].…”

“…However, 2-3 min of annealing at a temperature of about 160 °C causes a decline of several percent in the mechanical properties of the UFG material [21]. Annealing at a temperature above 200 °C leads to a significant decrease in microhardness in the case of 99.99% [26], 99.98% [27] pure copper and electrolytic tough pitch copper [23]. The energy accumulated in the material during SPD processing leads to a faster onset of recrystallization processes.…”