The High Temperature Degradation of Cd-Zn and Pb-Cd Eutectic Alloys

Abstract

Various thermal treatments have been applied to Cd-Zn and Pb-Cd eutectic alloys in an attempt to better understand the thermal stability of eutectics close to their melting temperatures. Specimens of each system were grown at 40, 400 and 4000 mm/hr to obtain microstructures which were either lamellar, lamellar/cellular, or cellular. These specimens were thermally treated by either: (1) isothermal annealing at 0.95 Tm (up to 192 hrs), (2) thermal cycling between room temperature and 0.95 Tm (up to 64 cycles), (3) exposing to thermal gradients parallel to the growth direction and maintaining one end of the specimen at 0.95 Tm and the opposite end at room temperature (up to 48 hrs). It was found in all cases that some microstructural changes occurred but that the two alloy systems displayed marked differences in degradation sequence. An explanation and interpretation of these decay sequences is attempted. The mechanical properties of the variouslytreated alloy specimens were determined and are correlated with the observed microstructural features. The Cd-Zn specimens coarsened more rapidly than equivalent Pb-Cd specimens, as might be expected since the interphase boundary energies have been reported as 86 and 67 erg/cm2 respectively.