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.

The work hardening behavior and deformed microstructure of the CuNiSi alloy aged at 723 K for various times and then deformed at 293 and 77 K were extensively investigated. The precipitate microstructure was also observed using transmission electron microscopy after aging treatment at 723 K for 0.30, 3.6, 64.8 and 345.6 ks. Deformation twins were clearly observed by transmission electron microscopy in the under-aged specimen deformed by 10% in tension at 293 K, in accordance with the enhanced work hardening rate observed during tensile deformation. The thickness of the deformation twins observed was approximately 140 nm. In addition, a significant fraction of larger deformation twins were observed by EBSD on the surface of the under-aged and peak-aged specimens tested at 77 K, for which the stressstrain behavior exhibited a nearly constant work hardening rate, i.e., high tensile strength and high elongation. These results show that the deformation twins formed during tensile deformation at 293 K contribute to strengthening of the specimen as new obstacles to the dislocation slip. Moreover, the enhanced twinning deformation at 77 K achieves high strength and elongation in the under-aged and peak-aged conditions. On the other hand, only a few deformation twins were observed in the supersaturated solid solution and over-aged specimens.

The aim of this study is to investigate a characteristic deformation behavior of a precipitation strengthening-type Cu-Ni-Si alloy (Cu-2.4Ni-0.51Si-9.3Zn-0.15Sn-0.13Mg) by microcompression specimens. Three micropillars with a square cross-section of 20 × 20 × 40 μm3 were fabricated by focused ion beam (FIB) micromachining apparatus and tested by a machine specially designed for microsized specimens. The three pillars were deformed complicatedly and showed different yield strengths depending on the crystal orientation. The micromechanical tests revealed work hardening by the precipitation clearly. Electron backscattered diffraction analysis of a deformed specimen showed a gradual rotation of grain axis at the grain boundaries after the compression test.

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