SUPERPLASTIC BEHAVIOR OF PB-SN EUTECTIC ALLOY

The superplastic behavior of PbSn eutectic alloy was investigated for grain sizes from 2.2 to 6.1 μm over a range of temperatures from 298 to 373 K and with strain rates from 10-7 to about 10-2 s-1. The results showed that the stress-strain rate relation can be divided into two distinct regions: (a) at strain rates lower than approximately 10-3 or 10-4 s-1 the stress exponent was 2.4, the inverse grain size dependence exponent was 1.6 and the true activation energy was 10.5 kcal mol-1; (b) at higher strain rates the stress exponent was 5.7, the strain rate was independent of grain size and the true activation energy was 20.8 kcal mol-1. At low strain rates an apparently distinct region characterized by a stress exponent equal to unity was observed when datum points were taken at strains between 0.2% and 3.5%. When datum points were taken at strains larger than 5% this region was not observed. © 1979.