ANALYSIS OF HYDROGEN-ATOM TRANSPORT IN A 2-PHASE ALLOY

The theoretical basis for analysing hydrogen atom transport in a two-p hase alloy is evaluated. Experimental measurements of hydrogen atom tr ansport in a duplex stainless steel, thermally treated to give a varyi ng volume fraction of austenite, are described and analysed to ascerta in the relative effect on the effective diffusivity of interfacial tra pping and of the reduced diffusivity but enhanced solubility of the au stenite phase. The effective diffusivity of the as-received duplex sta inless steel is a factor of 400 less than that for the fully ferritic steel. It is demonstrated that diffusion through the austenite has no effect on the hydrogen transport, despite the higher solubility of hyd rogen in this phase. However, the presence of austenite creates a more tortuous path for the hydrogen transport. The enhanced solubility of hydrogen atoms in the austenite phase, relative to that in the ferrite phase, can be considered to induce a trapping effect on the hydrogen atom transport; however, the effect is small relative to the trapping associated with the austenite-ferrite interface. The binding energy of the interfacial traps is estimated to be about 52 kJ mol-1.