Interactions of hydrogen with dislocations and passivating firms on Fe-based alloys have been studied. In the first, interaction of hydrogen with dislocations has been studied to differentiate between the two competing effects of mobile dislocations created during plastic deformation on the trapping and transport of hydrogen and to investigate effects of plastic deformation on the hydrogen permeation behaviours through 3.3 Ni - 1.6 Cr steel. In the second, interaction of hydrogen with passivating films on pure iron in 0.15 N $Na_2B_4O_7$ - 0.15 N $H_3BO_4$ solution (pH 8.4) has been studied to elucidate the role of hydrogen on the change of electrochemical properties of passivating films.
In chapter III, the apparent diffusivity and solubility of hydrogen were determined from the build-up and decay transients given by static permeation and dynamic straining permeation experiments. In order to make a clear distinction between hydrogen trapping and transport by dislocations, it is necessary to take the apparent diffusivity of hydrogen obtained from specimens involving approximately comparable dislocation structures and to compare them critically. The apparent diffusivity of hydrogen decreases the unstrained specimen, the 3.5 % - prior strained specimen followed by additional straining at strain rate of $5.2×10^{-6}$/s the 3.5 % - prior strained specimen followed by additional straining at strain rate of $1.0×10^{-6}$/s, and the 3.5 % - prior strained specimen in that order. The solubility of hydrogen increases due to the increase of strain during static permeation experiment. The present static and dynamic hydrogen permeation experiments permitted us to correlate the results with hydrogen trapping and transport effects of disllocations.
In chapter IV, effects of a concomitant plastic deformation on the hydrogen permeation behaviours through 3.3 Ni - 1.6 Cr steel have been investigated by using gas phase and galvanostatic hydrogen charging and electrochmical detection method at 29 C. The static steady state permeation flux decreases upon yielding and then the flux increases slightly after the strain of about 3.7 %. The deviation from the static steady state permeation flux during plastic deformation is larger for fast strain rate, and it becomes negligible by the deformation stop during plastic deformation. The hydrogen permeation flux obtained by dynamic permeation test decelerated the permeation flux compared to that obtained by static permeation flux and it showed the hump during the deformation. These results were well supported by the concept that the concurrent occurrence of two competing effects of hydrogen trapping and transport by dislocations.
In chapter V, effects of hydrogen on the breakdown of passivating films on pure iron in 0.15 N $Na_2B_4O_7$ - 0.15 N $H_3BO_4$ solution (pH 8.4) under applied potential of 300 mVsce have been investigated by measuring pitting initiation time as a function of input hydrogen pressure, Cl-ion concentration and the time of cl-ion addition after the stop of hydrogen injection and impedance of passivating films by using gas phase hydrogen charging at 30 C. Due to the injectionof hydrogen into passivating films, the breakdown of passivating films on pure iron is accelerated and the capacitance of passivating films increases at first and then slightly decreases. These results were well supported by the suggestion that the introduction of hydrogen into passivating films changed the oxidation state of passivating films by changing the ratio of hydrogen containing species to exygen ion in passivating films.
In chapter VI, the changes of passivating current of passivating films on pure iron in 0.15 N $Na_2B_4O_7$ - 0.15 N $H_3BO_4$ solution (pH 8.4) due to the potential changes within the passivaing range of potential have been investigated as a function of ageing time of passivating films and hydrogen injection. Passivating films formed on pure iron under the applied potential of 300 mVsce does not reach steady state in 3 days. Cathodic current is passed for a few moment in the case of potential drop from 650 mVsce to 300 mVsce. The effects of hydrogen injection and ageing time on the changes of current caused by potential changes are discussed in terms of the change of oxidation state in the passivating films due to the redox reaction of hydrogen containing species within the passivating films.
