A quantitative analysis of hydrogen trapping

Abstract

The complex hydrogen trapping characteristics of iron-titanium-carbon alloys, contain-ing both reversible and irreversible traps have been fully analyzed. The key to this quantitative analysis is a complete identification of the type and number of each operating trap. The trapping parameters were obtained from an analysis of the relevant hydrogen permeation transients. Titanium substitutional atoms have been shown to be reversible, low occupancy traps with an interaction energy with hydrogen,E (Ti-H), of 0.27 eV. Typi-cal rate constants for these alloys are; a hydrogen capture rate constant of approximately 10-24 cm3/atom .s a release rate constant of approximately 10-3 s-1 and a trapping rate of the order of 1015 atoms, H/cm3 .s. TiC particles are irreversible traps with a large oc-cupancy and an interaction energy, .E(TiC-H), of 0.98 eV. The irreversible trapping parameters are calculated from the first permeation transient, where mixed trapping oc-curs. The trapping kinetics are about an order of magnitude faster than when only rever-sible trapping exists. The role of trapping on the effective diffusivity of hydrogen is dis-cussed as is, briefly, its role in affecting hydrogen-induced damage. Finally, guidelines are given to permit the trapping behavior of more general alloys to be analyzed.