Blistering and Hydrogen Isotope Retention in Tungsten (pp. 311-334)
Authors: (W. M. Shu, ITER Organization, St. Paul-lez-Durance, France, and others)
Abstract: The behavior of hydrogen isotopes in metals has been one of the most important topics in physical metallurgy and solid-state physics with a broad range of technological implications for many decades [1, 2]. With respect to dissolution of hydrogen isotopes in metals, there are two sorts of metals, i.e., exothermic metals having strong affinity with hydrogen isotopes and endothermic metals with chemical potential of hydrogen isotope atom in the interstitial sites of metal lattice higher than that of half hydrogen isotope molecule in gaseous phase. The former includes titanium, uranium, zirconium and some rare metals. Typical examples of the latter are iron, nickel, tungsten, etc. The metallic hydrides are formed when the concentration of hydrogen isotope atoms in the interstitial sites of exothermic metals exceeds a certain value at a fixed temperature. The chemical affinity between the hydrogen isotopes and the metals determines the equilibrium pressure at a certain temperature and storage capacity of hydrogen isotopes in the metallic hydrides . On the contrary, no metal hydrides are formed in endothermic metals under normal conditions. The hydrogen isotope atoms may be trapped at defect sites such as vacancies and grain boundaries to form hydrogen bubbles, which is the major mechanism of hydrogen embrittlement of metals.