DISLOCATION INTERNAL-FRICTION INVESTIGATION IN HIGH-PURITY COLD-WORKED TANTALUM

After a low temperature deformation of high purity tantalum, an internal friction apparatus permits the measurement of the torsion plastic strain versus temperature as well as internal friction and modulus change. This kind of observation shows that in an intermediate temperature range (230 to 350 K) the glide on the {211} plane becomes active, and that the HCW-peak presents a sub-structure that can be revealed by some deformation and annealing procedure in this temperature range. The morphology of this ,,intermediate'' dislocation microstructure is characterized by long screw-dislocations with long kinked segments associated to jogs of considerable height. The HCW2-peak which appears after ageing in the 230 to 350 K range, is due to the {110} kink diffusion of long kinked segments on screw dislocations and the HCW1-peak is caused by KPF on 71-degrees-edge-dislocations formed by the annealing above 400 K.