Twinning induced plasticity and work hardening behavior of aged CuNiSi alloy

Abstract

The work hardening behavior and deformed microstructure of the CuNiSi alloy aged at 723K for various times and then deformed at 293 and 77K were extensively investigated. The precipitate microstructure was also observed using transmission electron microscopy after aging treatment at 723K 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 293K contribute to strengthening of the specimen as new obstacles to the dislocation slip. Moreover, the enhanced twinning deformation at 77K 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. © 2014 The Japan Institute of Metals and Materials.