Dislocation sub-structures, recovery and recrystallization in pure tantalum

Abstract

Plastic deformation, static recovery and recrystallization in pure tantalum are analyzed in the present paper. Quantitative analysis of dislocation sub-structures were done. Sub-structures development is completely dependent on crystallographic orientation. No clear effect of recovery was observed when direct analysis was made. Hence, recovery was studied through its effect on recrystallization. Recovery heat treatments followed by a recrystallization heat treatment were applied to compare the recrystallized state of samples which were subject to prior recovery with those which were not. Results show that recrystallization is accelerated in the early stages of recovery (low temperature or low annealing time or low plastic strain). On the opposite, in the advanced stages of recovery, it slows down recrystallization. Results show again an influence of crystallographic orientation. Static recrystallization was also investigated and the influence of crystallographic orientation, most probably inherited from the deformed state through dislocation sub-structures, was observed. Based on experimental results, a discussion on the mechanisms of nucleation in the different orientation grains is presented. Finally, a discussion is made on the quantification of stored energy. The effect of the observation scale and the choices of considering dislocation density or dislocation sub-boundaries energies from EBSD data is discussed.