Samples of 4N-purity copper and nickel of 4N8-purity were deformed in high-pressure torsion at different hydrostatic pressures, to different shear strains. Activation enthalpies (Q) were determined by differential scanning calorimetry using Kissinger’s method. For the one annealing peak found in high-pressure torsion Cu, Q amounts to 0.78 to 0.48eV; depending upon the shear strain applied. In the case of Ni, the activation enthalpies of the two annealing peaks were determined to be Q = 0.65eV and Q = 0.95eV, respectively, with no obvious dependence upon shear strain, although this was indicated by the annealing peak temperatures. Applying defect specific analyses of the annealing peaks, it turned out that the larger Q value represents the annihilation of dislocations and agglomerates, while the smaller one reflects the annihilation of single or double vacancies. Concerning the strain dependence of the larger Q, two possible explanations were discussed: (1) the annihilation of dislocations assisted by the strain-dependent density of vacancy agglomerates and (2) the annihilation of dislocations enhanced by a strain-dependent level of long-range internal stresses. Because of closer correlations of Q with external and internal stresses at very high shear strains, explanation (2) was favored.

Activation Enthalpies of Deformation-Induced Lattice Defects in Severe Plastic Deformation Nanometals Measured by Differential Scanning Calorimetry. D.Setman, M.B.Kerber, E.Schafler, M.J.Zehetbauer: Metallurgical and Materials Transactions A, 2010, 41[4], 810-5