EFFECT OF PHASE-TRANSFORMATION ON CREEP CHARACTERISTICS OF SN-5 WT-PERCENT BI ALLOY

The creep characteristics of Sn-5 wt% Bi alloy have been investigated under different constant ap plied stresses ranging from 26.8 to 29.4 M Pa 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 beta and n were calculated an d found to change with the applied stresses from 1.8 x 10(-6) to 6.36 x 10(-5) and from 0.53 to 0.98, respectively. The strain rate sensitiv ity parameter (m) was found to change from 0.071 to 0.093 which charac terizes a dislocation mechanism. The activation energy of the transien t creep amounted to 17 and 33 kJ/mol before and after the transformati on temperature, due to both glide of dislocations and cross slipping d islocation mechanism, respectively. The activation energies of the ste ady state creep in the vicinity of the transformation and above the tr ansformation temperature were found to be 62 and 87 kJ/mol as characte ristic of the grain boundary sliding mechanism. The analysis of the X- ray diffraction patterns of the alloy samples confirmed all the above- mentioned mechanisms.