Physical mechanisms of helium release during deformation of vanadium alloys doped with helium atoms

Abstract

Helium embrittlement of vanadium alloys which are labored for future fusion reactors may be closely related to the transport of helium to critical failure sites within the material (grain boundaries, precipitates, etc.). Recently during high-temperature mechanical tests of helium-doped vanadium alloys by the tritium trick technique, the abnormal helium release peaks have been observed. In this case, a good correlation has been found between the helium release during the deformation and embrittlement processes. Such results have fundamental meaning for understanding the helium behavior during deformation of fusion structural materials. In the present paper, the physical mechanisms of abnormal helium release from deforming vanadium alloys are suggested. The theory of helium release is based on the dynamic-diffusion models of dislocation motion with helium atoms and helium bubbles, where helium atoms and helium bubbles are swept by moving dislocations. In the suggested model, the effect of the strain rate of plastic deformation and pipe diffusion of helium atoms along dislocations on this phenomenon is considered. The theoretical models are compared with experimental results for helium release during deformation of vanadium alloys after helium doping by the tritium trick technique. The temperature dependence of this phenomenon and the effect of strain rate on growth kinetics of helium bubbles are analyzed. The present results allow us to understand the effect of various helium doping techniques (helium trick, cyclotron preimplantation and boron-10 technique) on helium release from deformed vanadium alloys.