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The University of Southampton

Research project: Processing of a two phase alloy by severe plastic deformation

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The Pb-62% Sn eutectic alloy is widely used in the manufacturing of electronic products and it also has exceptional superplastic properties. By producing the alloy through severe plastic deformation (SPD) techniques, the grain size of the alloy can be reduced to the submicrometer level and superplasticity is significantly improved. Additionally, microstructural evolution of the Pb-Sn alloy is investigated to provide information on a representative two-phase alloy processed by SPD.

The grain size of metallic alloys may be refined to the submicrometer level by using processing SPD techniques such as equal-channel angular pressing (ECAP) and high-pressure torsion (HPT). In ECAP the sample is in the form of a bar and it is subjected to repetitive pressing through a special die whereas in HPT the sample is in the form of a disk and it is subjected to an applied pressure and concurrent torsional straining.  Little information is at present available comparing the microstructures and the mechanical properties of two-phase alloys processed using these two techniques. This investigation is designed to make a direct comparison between ECAP and HPT using a typical two-phase alloy and it involves materials processing, mechanical testing and microstructural analysis.

The Pb-62% Sn eutectic alloy is a classic superplastic material exhibiting a record superplastic elongation of 7550%. The reason for this exceptional elongation is that grain growth is restricted by the presence of two separate phases. In this project, the Pb-Sn eutectic alloy is processed with ECAP or HPT or by using a combination of these two methods (ECAP+HPT) and the microstructural characteristics and mechanical properties are then measured.

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