DEFECT PARAMETERS OF B.C.C. METALS - GROUP-SPECIFIC TRENDS

Defect parameters of atomic defects ("point defects") and properties of dislocations as expressed in the kink model are summarized. For the evaluation of point defect properties the author adopts the vacancy interpretation of stage III recovery. The collected defect parameters show pronounced group-specific trends depending upon the electron-to-atom ratio. The mobility of vacancies as well as of screw dislocations can be correlated with the elastic properties. This holds for both alkali and transition metals. Reference is made to recent theoretical and experimental work of other authors, where it has been shown that the variation of binding forces with the filling of d states, characteristic phonon anomalies, phase stability as well as the "anomalous self-diffusion" in the titanium group metals are strongly inter-related. A suggestion is made for the vacancy configuration in ferromagnetic iron which could resolve apparent inconsistencies. Results for self-interstitial atoms are more difficult to evaluate. The observation of long-range migration, even near 4 K, in alkali and group 5 metals is remarkable. For group 6 metals the low temperature recovery can be explained by planar migration of the self-interstitial atom. The impact of group-specific defect properties for the processing of refractory metals is outlined briefly.