EXPERIMENTAL STUDIES ON HYDROGEN DIFFUSION AND TRAPPING IN MARTENSITIC AND AUSTENITIC STAINLESS-STEELS FOR FUSION APPLICATION

In the development of materials for the first wall and blanket, the presence of hydrogen, its permeation and the possible degradation of mechanical properties represent a key issue. This article presents experimental methods and results concerning measurement of the diffusion coefficient, of the critical concentration for hydrogen-induced cracking and determination of the amount and binding energy of traps for several steels of interest for nuclear fusion, among them Manet. The diffusion coefficient measurements were conducted electrochemically or by high temperature thermal analysis and data were extended, on the basis of the trap's theory, to a temperature range of considerable importance for nuclear fusion applications. With respect to the materials studied, analytical correlations are provided which describe the diffusion and trapping of hydrogen. The tests on the critical concentration of hydrogen are also presented and discussed. In the case of Manet these tests highlighted strong dependence of this parameter on the microstructure.