Impression creep behavior of cast Pb-Sb alloys

Creep behavior of the cast the Pb-1.25%Sb and Pb-4.5%Sb alloys was studied by impression testing. The tests were carried out under constant stress in the range of 40-135 MPa and at temperatures in the range of 300-420 K. Assuming a power law relationship between the impression velocity and stress, power law stress exponents of 3.3 and 12.5 were obtained for Pb-1.25%Sb at low and high stresses, respectively. These stress exponents for the Pb-4.5%Sb alloy were found to be 4 and 19 in the similar stress and temperature ranges. Analysis of the data showed that for all loads and temperatures, the activation energy for both materials was stress-independent with an average value of 63 U mol(-1). Based on the obtained stress exponents and activation energy data, which is very close to 65.6 kJ mol(-1) for Pb diffusion in the Pb grain boundaries, it is proposed that in the low stress regime the operative creep mechanism is grain boundary diffusion. This behavior is in contrast to the high stress regime in which, the stress exponents of 12.5 and 19 are indicative of a dislocation creep mechanism in both alloys. (c) 2006 Elsevier B.V. All rights reserved.