Materials Transactions Online

Materials Transactions, Vol.55 No.03 (2014) pp.501-505
© 2014 The Japan Institute of Metals and Materials

Twinning Induced Plasticity and Work Hardening Behavior of Aged Cu-Ni-Si Alloy

Akiyoshi Araki1, Warren J. Poole2, Equo Kobayashi1 and Tatsuo Sato3

1Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, Tokyo 152-8552, Japan
2Department of Materials Engineering, The University of British Columbia, Vancouver V6T 1Z4, Canada
3Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan

The work hardening behavior and deformed microstructure of the Cu-Ni-Si 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 1-40 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 stress-strain 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.

(Received 2013/10/15; Accepted 2013/11/25; Published 2014/02/25)

Keywords: copper nickel silicon alloy, work hardening, twinning induced plasticity, precipitation hardening, electron microscopy

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