BOUNDARY SLIDING BEHAVIOR IN HIGH-PURITY PB-62-PERCENT SN

Boundary sliding behaviour in high-purity Pb-62% Sn containing 5 ppm o f impurities has been investigated in tension at T = 422 K by measurin g the individual offsets across boundaries. In the investigation, the alloy was tested at various initial strain rates, in the range of 5.33 x 10(-7) to 1.33 x 10(-1) s(-1). The experimental results show that t he contribution of boundary sliding to total strain at low strain rate s is significant (about 60%) and comparable to that at intermediate st rain rates (the superplastic region in alloys of high impurity levels) . Also, the results reveal that, in general, there is no considerable difference in the average value of sliding offsets at the three types of boundary: Pb-Pb, Sn-Sn and Pb-Sn. However, contribution of sliding at interphase boundaries, Pb-Sn, appears to be more significant than t hat at intercrystalline boundaries, Pb-Pb and Sn-Sn. The above results are discussed in the light of recent data regarding the effect of imp urities on superplastic flow.