(A) study on the hydrogen diffusion and hydrogen trapping in crystalline and amorphous metallic alloys

Abstract

The trapping and diffusion behaviors of hydrogen in crystalline metals and amorphous alloy have been investigated by using the hydrogen thermal analysis technique. In part one, the concept and existing theories of trapping of hydrogen in metals are introduced. Also the relations between the hydrogen trapping and embrittlement are examined. Theoretical backgrounds of the hydrogen thermal analysis method and the methods measuring the trapping parameters like trap activation energy and trap binding energy are explained. In part two, the effects of the character of the precipitated TiC/matrix interface on the hydrogen trapping behavior in steel is studied. A model for hydrogen trapping of particle-matrix interface is suggested, in which the large driving force for such hydrogen trapping is associated with the lowering of interfacial free energy. Incoherent titanium carbides have a larger trap activation energy of hydrogen than semi-coherent ones. Although the particles are incoherent, the trap activation energy of hydrogen increases with increasing the precipitated particle size. In part three, the trapping of hydrogen in thoria dispersed nickel has been investigated. The voids are formed at the particle-matrix interface during cold work. Annealing at high temperature removes this extra trapping sites, allowing an intrinsic trapping effect due to thoria particle matrix interface to be measured. The trap binding energy and trap activation energy of hydrogen at the interfaces of $ThO_2$/lattice are estimated as 33kJ/mol and 48.7kJ/mol, respectively, which indicates that trapping into thoria matrix interface is relatively easy. In part four, the hydrogen trapping behavior by voids in nickel is studied. Voids in nickel act as strong trapping site for hydrogen. It appears that hydrogen in the void exists as a gas phase and chemisorbed state. However, under the condition investigated in this work, i.e. the temperature range of 623 K to 855 K and 1 atm $H_2$ pressure, mos...