High Strength and Good Ductility in Cu-3Ag-0.5Zr Alloy by Cryo-Rolling and Aging
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JMEPEG DOI: 10.1007/s11665-016-2419-3
High Strength and Good Ductility in Cu-3Ag-0.5Zr Alloy by Cryo-Rolling and Aging S. Chenna Krishna, Niraj Chawake, Ravi Sankar Kottada, Abhay K. Jha, Bhanu Pant, and P.V. Venkitakrishnan (Submitted August 5, 2016; in revised form September 29, 2016) A combination of high strength and good ductility was achieved in a precipitation hardenable Cu-3Ag0.5Zr alloy through cryo-rolling (80% reduction in thickness) and aging in the temperature range (200500 °C). The high-strength sheets produced by cryo-rolling showed a threefold increase in yield strength compared to that of the solution-treated and aged (220 MPa) sample, while retaining good ductility. An optimum combination of high strength (614 MPa) and ductility (8%) was achieved by 80% cryo-rolling and aging at 320 °C for 1 h. The high strength and good ductility obtained was attributed to various microstructural factors such as deformation twins, ultra-fine grains, high dislocation density and fine nanosized silver precipitates. Keywords
aging, cryo-rolling, Cu-Ag-Zr alloys, high strength
1. Introduction Materials with high strength and ductility are desirable for structural applications. However, there is always a trade-off between these two properties. Hence, it is quite challenging to achieve such a combination. In this connection, bulk ultra-finegrained (UFG) materials were extensively studied in the recent past because of their high strength (Ref 1). The UFG materials can be produced in bulk by several severe plastic deformation (SPD) techniques such as equal channel angular pressing (ECAP), accumulative roll bonding (ARB), severe torsion stressing, groove pressing and cryo-rolling (Ref 1, 2). Further, there are several reports documenting the realization of high strength and ductility through the combination of SPD methods and annealing/aging (Ref 3-9). Nevertheless, most of the materials studied were pure metals (Ref 10, 11), aluminum alloys (Ref 3, 12-14) and solid solution-strengthened copper alloys (Ref 15-20). Table 1 and Fig. 1 present the key results from the previous studies that deal with a combination of high strength and ductility in pure copper and Cu-based alloys. The high ductility and strength achieved in these materials was attributed to bimodal grain size distribution (Ref 21-23), high-angle grain boundaries (HAGBs) (Ref 22, 24), deformation twins (Ref 18, 24), fine precipitates (Ref 7, 14, 25, 26) and homogenous microstructure (Ref 7, 26). Among the SPD methods employed to achieve high strength, accumulative roll bonding (ARB), cryo-rolling (CR) and high-pressure torsion (HPT) resulted in yield strength higher than 700 MPa (Ref 2731). Nevertheless, high strength was also reported in Cu-3Ag
S. Chenna Krishna, Abhay K. Jha, Bhanu Pant, and P.V. Venkitakrishnan, Materials and Mechanical Entity, Vikram Sarabhai Space Centre, Trivandrum 695 022, India; and Niraj Chawake and Ravi Sankar Kottada, Department of Metallurgical and Materials Engineering, IIT Madras, Chennai 600 036, India. Contact e-mail: chenna.sk@g
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