AN INVESTIGATION OF THE ROLE OF INTRAGRANULAR DISLOCATION STRAIN IN THE SUPERPLASTIC PB-62-PERCENT SN EUTECTIC ALLOY

Experiments were conducted on the Pb-62% Sn eutectic alloy to determine the role of intragranular dislocation movement in the superplastic region II. By taking careful measurements within individual grains of a specimen tested at 423 K at a strain rate near the center of region II, it is demonstrated that there is evidence for the movement of some intragranular dislocations, but the strain is non-uniform and oscillatory in nature with changes from positive to negative contributions to the total strain as the deformation continues. The results show that the Sn and Pb phases behave similarly and the net contribution to the total strain is close to zero. It is concluded that grain boundary sliding and the relative translation of individual grains represents the dominant flow mechanism, and intragranular dislocation movement occurs as an accommodation process which, nevertheless, has an important influence on the flow mechanism because it represents a source of mobile extrinsic grain boundary dislocations.