After studying the various fundamental mechanisms that could control the plastic deformation of a bcc metal at low temperatures, it was shown that two models (Peierls-Nabarro, Escaig-Hirsch) permitted a satisfactory interpretation of the plastic behavior of polycrystalline Nb at low temperatures. The two models led to a linear relationship between activation energy and temperature. The results were in agreement with this conclusion up to 195 or 210K, according to the purity of the metal. The low values found for the activation volume (less than 10b3), confirmed that it was related to an intrinsic frictional resistance to the movement of dislocations. The values of line tension and critical distance between kinks, calculated from the Peierls-Nabarro model, were identical for the four purities examined and were perfectly compatible with published values for other body-centered metals such Fe, Ta and V. On the basis of the Escaig-Hirsch model, an approximate value of the stacking-fault energy of about 90mJ/m2 was obtained.

Mécanismes de Déformation du Niobium Non-Allié à Basse Temperature. J.F.Fries, B.Houssin, G.Cizeron, P.Lacombe, Journal of the Less Common Metals, 1973, 33[1], 117-52