Strain weakening and superplasticity in a Bi-Sn eutectic alloy processed by high-pressure torsion

High-pressure torsion (HPT) was conducted on disks of a Bi-Sn eutectic alloy under a pressure of 6.0 GPa. The microstructural evolution was studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Measurements of Vickers microhardness showed decreasing strength caused by strain weakening after HPT processing. Tensile testing was performed under initial strain rates from 10(-4) to 10(-2) s(-1) at room temperature. The results demonstrate a much improved elongation to failure for the Bi-Sn alloy after HPT-processing. The Bi-Sn alloy processed through 10 turns gave an elongation to failure of more than 1200% at an initial strain rate of 10(-4) s(-1) at room temperature which is significantly larger than the elongation to failure of similar to 110% in the as-cast Bi-Sn alloy under the same tensile conditions.