The creep characteristics of Sn—5 wt% Bi alloy have been investigated under different constant applied stresses ranging from 26.8 to 29.4 MPa and at different temperatures ranging from 305 to 373 K. Results of both transient and steady state creep indicated one transition point at 328 K. The transient creep parameters β and n were calculated and found to change with the applied stresses from 1.8 × 10−6 to 6.36 × 10−5 and from 0.53 to 0.98, respectively. The strain rate sensitivity parameter (m) was found to change from 0.071 to 0.093 which characterizes a dislocation mechanism. The activation energy of the transient creep amounted to 17 and 33 kJ/mol before and after the transformation temperature, due to both glide of dislocations and cross slipping dislocation mechanism, respectively. The activation energies of the steady state creep in the vicinity of the transformation and above the transformation temperature were found to be 62 and 87 kJ/mol as characteristic of the grain boundary sliding mechanism. The analysis of the X‐ray diffraction patterns of the alloy samples confirmed all the above‐mentioned mechanisms.

The effect of plastic deformation on the microstructure of heat treated superplastic alloy samples (Sn–5wt% Bi) prepared at two different rates of cooling 1.77 × 10–3 K/s and 18.4 K/s, named as slowly cooled and quenched in liquid nitrogen samples, have been studied as a function of temperature in the range of 308–388 K. The work hardening parameters for the two alloy samples were found to be dependent on both temperature and cooling rate. These parameters indicate the transition temperature at 328 K. The slowly cooled samples are much harder than those quenched in liquid nitrogen. This is explained by precipitation of Bi‐atoms which segregate to form a non‐coherent cubic α‐phase in the slowly cooled samples. The activation energy for fracture of the Sn–5wt% Bi alloy is divided into three stages with values of 19.2 ± 1.6, 18.7 ± 1.4 and 10.9 ± 0.81 kJ/mol and 15.6 ± 1.9, 14.6 ± 1.8 and 7.9 ± 1.1 kJ/mol for the slowly cooled and quenched alloy samples, respectively. The lattice parameters (a, c), the ratio (c/a) and the residual lattice strains (Δa/a, Δc/c) are found to be dependent on the test temperature and the rate of cooling with either maximum or minimum values at the transition temperature. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Sn-3.5wt.%Ag-0.5wt.%Cu is one of the alloys considered for replacing SnPb solder alloys in electronic ambiance. In the present study, the effect of minor additions of Ti (0.25, 0.5, 1.0 wt.%) on the microstructure, creep and thermal properties of Sn-3.5wt.%Ag-0.5wt.%Cu lead free solder alloy are investigated by means of scanning electron microscopy (SEM), x-ray diffraction (XRD), creep tests and differential scanning calorimetry (DSC) thermal tests. Results showed that the addition of different wt.% of Ti refined the grain size of the solder alloys. The microstructure parameters obtained from x-ray analysis represented by lattice parameters (a,c), axial ratio (c/a), residual strains (?a/a? & ?c/c?), peak height intensities and crystallite size of some crystallographic planes were found to be sensitive to Ti - additions, applied stresses and working temperatures. The morphological studies using SEM showed refinements of Ag3Sn, Cu6Sn5 and Ti2Sn3 (IMCs) in ?-Sn matrix. Thermal analysis showed that Ti - additions slightly affect melting temperature and pastry range. In terms of creep behavior the addition of 1wt.%Ti gave the highest creep resistance with respect to the others, due to fine dispersion of IMCs. The stress exponents (n) and the activation energies (Q) indicated that the dominant creep mechanism is dislocation climb over all temperature ranges