Impression creep behavior of lead-free Sn–5Sb solder alloy

Abstract

Creep behavior of the lead-free Sn–5Sb solder alloy in the cast and wrought conditions was investigated by impression testing. The tests were carried out under constant stress in the range of 18–135 MPa and at temperatures in the range of 298–403 K. Assuming a power law relationship between the impression rate and the punching stress, stress exponents of 2.8 and activation energies of 41.3 kJ mol −1 were determined for the wrought material over the whole stress and temperature ranges studied. For the cast condition, however, stress exponents of 5.4 and 11.4 and activation energies of 53.8 and 75.8 kJ mol −1 were obtained at low and high stresses, respectively. The n value of 2.8 and the activation energy of 41.3 kJ mol −1, which is very close to the activation energy for grain boundary diffusion of β-Sn, together with a very fine grain size of 4.5 μm and a uniform distribution of fine SnSb particles, may suggest that grain boundary sliding is the dominant creep mechanism in the wrought condition. For the cast material with a coarse grain size of 280 μm, the low stress regime activation energy of 53.8 kJ mol −1, which is close to that of the self diffusion of pure Sn, and a stress exponent of 5.4 suggest that the operative creep mechanism is dislocation climb. This behavior is in contrast to the high stress regime in which, the n = 11.4 and Q = 75.8 kJ mol −1 are indicative of a dislocation creep mechanism.