Abstract
An apparatus permitting extensive plastic deformation of wires of high melting point b.c.c. metals at liquid helium temperatures is described. The recovery of the electrical resistivity of pure and oxygen-doped tantalum deformed at liquid helium temperatures was measured up to 540 K. In this temperature interval, only one major recovery stage super-imposed on a continuous background recovery and located between 240 and 300 K was found. It is controlled by the longrange migration of an intrinsic point defect with a migration enthalpy of 0.70 ± 0.03 eV. The results are discussed in the context of high temperature and irradiation data, and it is concluded that the defect migrating in this “stage III” is a self-interstitial configuration. The rate theory of the annihilation of migrating point defects with their antidefects and simultaneous reactions with unsaturable sinks (dislocations) is developed in a form that permits the quantitative analysis of the isothermal recovery curves. Its application to the present experiments gives highly consistent results and strengthens the above conclusions. The close analogy between the point defect phenomena in tantalum and α-Fe is discussed.
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