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

Chuan Ting Wang,Terence G Langdon

doi:10.1088/1757-899x/63/1/012107

Abstract

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 ~110% in the as-cast Bi-Sn alloy under the same tensile conditions.

Highlights

Superplasticity refers to the exceptionally high elongations to failure, normally larger than 400%, that may occur in some metallic alloys under tensile conditions [1]
Some pitting holes were observed in the Bi-rich phase which remained because Sn particles were etached away by the etachant
Using an initial strain rate of 1.0 × 10-4 s-1, processing by 10 turns of High-pressure torsion (HPT) produced a sample with an elongation to failure of ~1200% which is an improvement of more than ten times compared with the elongation to failure of ~110% recorded in the as-cast and unprocessed alloy when testing at the same strain rate

Summary

Introduction

Superplasticity refers to the exceptionally high elongations to failure, normally larger than 400%, that may occur in some metallic alloys under tensile conditions [1]. The Bi-Sn eutectic alloy was extruded and aged for 7 days and an impressive elongation to failure of ~1950% was achieved when the sample was tested under a constant stress of ~250 lb·inch-2 (~1.7 MPa).

Results

Conclusion