Abstract
Equal-channel angular pressing (ECAP) was utilized to process a Bi-42Sn eutectic alloy at room temperature using processing route A for 1, 2, 4, and 8 passes. Tensile testing was performed at room temperature under initial strain rates in the range of 1.0 × 10−5 to 1.0 × 10−2 s−1. The results demonstrate that processing by ECAP improves the ductility in this material and the elongations to failure increased with decreasing strain rate in all samples. The largest elongation to failure, ~1300%, was recorded in the sample processed by ECAP for 8 passes at an initial strain rate of 1.0 × 10−5 s−1. This elongation is much improved by comparison with the as-cast Bi–42Sn alloy.
Highlights
The ability of a polycrystalline material to exhibit, in a generally isotropic manner, very high elongations prior to failure is known as superplasticity
Representative plots of engineering stress against elongation to failure are demonstrated in Fig. 1 for the samples processed by Equal-channel angular pressing (ECAP) for 8 passes, aged at room temperature for 40 days and pulled to failure at room temperature under different initial strain rates
Processing by ECAP leads to an increase in the elongation to failure and samples processed to higher numbers of ECAP passes show higher elongations to failure
Summary
The ability of a polycrystalline material to exhibit, in a generally isotropic manner, very high elongations prior to failure is known as superplasticity. Superplasticity is a diffusion-controlled process and it requires a relatively high testing temperature, typically at or above 0.5Tm where Tm is the absolute melting temperature of the material [1]. In addition to high testing temperatures, the materials should have a small and stable grain size, typically smaller than ~10 μm, to exhibit superplastic flow [2]. The reason is that it is hard for both of the two necessary conditions of superplasticity to be satisfied simultaneously in pure metals and solid solution alloys since grain growth occurs at high temperatures
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