Deformation Behavior of Pure Cu and Cu-Ni-Si Alloy Evaluated by Micro-Tensile Testing

Abstract

Micro-tensile tests of pure copper and a precipitation strengthening-type Cu alloy, Cu-Ni-Si alloy, were performed using micro-sized tensile specimens with 10 × 10 µm 2 in cross-section and 40 µm in length and a micro-gripper, which were fabricated by a focused ion beam system. The obtained experimental results were compared with the results of Cu-Ni-Si alloy bulk sample. The micro-tensile tests of both pure Cu and Cu-Ni-Si alloy showed the typical serrations caused by moving of dislocations and a decrease of ow stress by the necking. In the CuNi-Si alloy, characteristic deformation of work-hardening was observed. Electron back scatter diffraction analysis showed a gradual change in crystal orientation at the necking area.

Heterogeneous Deformation Behavior of Cu-Ni-Si Alloy by Micro-Size Compression Testing

“…In SIM images of all of the deformed micropillars, thin, curvy and numerous slip lines with some small protrusion were observed. This tendency was also observed in pure Cu specimen which grains were constrained by grain boundaries [15].…”

“…In the microtensile study [15], typical serrations during the plastic deformation were observed in the S E -S E curve. However, in the compression test, serrations were not observed and the curve is similar to the results obtained with a bulk specimen.…”

“…For the Cu-Ni-Si alloy, a heat treatment process was conducted first. The heat treatment process involved homogenization at 1223 K for 18 ks, cold rolling for 90% in thickness reduction rate and solution treatment process at 1123 K for 600 s. In order to reveal the effect of the precipitation, aging at 723 K for 300 s was performed, where the temperature and time needed for the precipitation hardening were determined in previous studies [13,15]. The grain size of the Cu-Ni-Si alloy was about 30 µm.…”

“…The difference in the yield stress was caused by dominantly crystal orientation difference, grain boundary, grain size and specimen size effect. In our previous work, the influence of orientations on mechanical properties of the microsized specimens of pure Cu was magnified with reduction of the number of grains inside a sample [15]. This size effect leads to scatter of experimental data of mechanical properties and can be quantified by the ratio between the specimen size: S and average grain size: G, denoted as S/G [19,20].…”

“…In our previous studies, we reported microtensile tests of a pure copper and a Cu-Ni-Si alloy with microtensile specimens fabricated by focused ion beam (FIB) milling system. In the microtensile tests, both of the specimens showed characteristic large serrations during deformation, which were not observed in the bulk samples, and the obvious necking deformation led to a decrease in the flow stress [15]. For deep understanding of micromechanical behavior in precipitate strengthened metals, comparisons of the results obtained from compression and tensile tests would be valuable to understand mechanical properties of the alloys in microscale in order to utilize them to the micro-or nano-electromechanical systems.…”