An investigation of intercrystalline and interphase boundary sliding in the superplastic Pb-62% Sn eutectic

Abstract

An investigation of boundary sliding in the superplastic Pb-62% Sn eutectic alloy shows that the contribution from sliding is high in the superplastic region II ( ϵ gbs ϵ t − 50–60%, where ϵ gbs is the strain due to sliding and ϵ l is the total strain), but there is a decrease in the magnitude of sliding in the less superplastic regions I and III ( ϵ gbs ϵ l − 20%) . A series of detailed measurements of boundary offset and type of interface indicates that the three boundaries in Pb-62% Sn exhibit very significant differences in sliding behavior: the largest sliding offsets occur at the Sn-Sn intercrystalline boundaries, smaller offsets are recorded at the Pb-Sn interphase boundaries and there is little or no sliding at Pb-Pb intercrystalline boundaries. No theory of superplasticity is available which satisfactorily accounts for either the decrease in ϵ gbs ϵ l in region I or the variation in average sliding offset at the three types of boundary. The results are consistent with earlier reports, from cavitation studies, that the various interfaces in a microduplex alloy exhibit different susceptibilities to cavity formation.