Doping-induced simultaneous improvement of strength and ductility in ultrafine grained gold wires
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C.C. Wong School of Materials Engineering, Nanyang Technological University, Singapore 639798
C.D. Breach and F. Wulff Materials and Applications Center, Kulicke & Soffa (S.E.A.) Pte. Ltd., Singapore 569871
T.Y. Lew School of Materials Engineering, Nanyang Technological University, Singapore 639798 (Received 10 February 2006; accepted 19 May 2006)
The room temperature tensile properties of ultrafine-grained 25-ā®m gold wires were evaluated as a function of calcium (Ca) doping at various strain rates ranging between 10ā3 and 10ā1 sā1. Paradoxically, the increased amount of Ca was found to simultaneously increase the strength and ductility of the Au wires. However, based on scanning electron microscopy and tensile characterization, the grain size distributions, strain-hardening rate, and strain rate sensitivity of Au wires did not change with Ca, thus showing that neither grain refinement nor plastic instability are likely to be responsible for the concurrent improvement of strength and ductility.
I. INTRODUCTION
It has been anticipated that with the drastic reduction of grain size, the strength and ductility of structural materials will be significantly improved. This has been the driving force behind increasing research efforts on the mechanical properties of ultrafine-grained (UFG) and nanocrystalline (NC) materials. Typical NC materials are characterized by grain sizes of
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