The effect of electric-current pulses on the evolution of microstructure and texture in cryogenically rolled copper was determined. The pulsed material was found to be completely recrystallized, and the recrystallization mechanism was deduced to be similar to that operating during conventional static annealing. The microstructural changes were explained simply in terms of Joule heating. A significant portion of the recrystallization process was concluded to have occurred after pulsing; i.e., during cooling to ambient temperature. The grain structure and microhardness were shown to vary noticeably in the heat-affected zone (HAZ); these observations mirrored variations of temper colors. Accordingly, the revealed microstructure heterogeneity was attributed to the inhomogeneous temperature distribution developed during pulsing. In the central part of the HAZ, the mean grain size increased with current density and this effect was associated with the temperature rise per se. This grain size was slightly smaller than that in statically recrystallized specimens.

The superplastic flow behavior of a near-γ titanium aluminide (Ti-45.5Al-2Cr-2Nb) is determined under uniaxial tension in as-rolled or rolled-and-heat treated conditions (1177°C/4 hr or 1238°C/2 hr). Cavitation characteristics, including cavity growth rates, are established via isothermal, constant strain rate tests conducted at 10−4 to 10−2 s−1 and temperatures between 900°C and 1200°C. Differences in cavitation as a function of initial structure, strain, strain rate and temperature are noted. Cavity growth is found to be largely plasticity controlled. Experimental growth rates are compared with equations that predict rates as a function of strain rate sensitivity. Although the equations assume no coalescence and no nucleation of new cavities, which are experimentally observed, they are useful in predicting actual growth rates.