Abstract
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 (Δ__a/a__, Δ__c__/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)