Influence of the P content on the transport parameters of hydrogen in Fe alloys

Abstract

In this work, the hydrogen transport parameters of permeability (ϕ), diffusivity (D) and Sieverts’ constant (KS) were experimentally measured in four Fe alloys supplied by the European Fusion Development Agreement (EFDA), by means of the gas evolution permeation technique. The samples had controlled chemical alloying element contents and microstructure. The experimental temperature range explored was from 423K to 823K and the high purity hydrogen loading pressures from 103Pa to 1.5·105Pa.The main objective of this work was to determine the influence of the P content of the alloy in the transport parameters of hydrogen. Two of the samples, pure Fe and FeC, contained negligible quantities of P (less than 5ppm in weight), whereas the other two, FeP and FeCP, had the same metallurgical composition as their corresponding pair, with the only difference in the phosphorus content (89ppm in weight and 88ppm in weight, respectively).The experimental permeation results were analyzed using a non-linear least square fitting. The final resulting values of the aforementioned transport parameters were paired off in order to determine the effect of the P content: pure Fe versus FeP and FeC versus FeCP. We observed that the permeability obtained for all the samples follows an Arrhenius law in each case. In general terms, the increase of the P content in the alloy leads to smaller values of the permeability showing a decrease in the permeation activation energy. Regarding diffusivity and Sieverts’ constant, trapping effects have been observed for the alloys containing P. This phenomenon was detected at temperatures below 473K. According to the results, the influence of the metallurgical composition of P in Fe alloys in the transport parameters of hydrogen is studied together with the synergistic effects caused by the presence of C.