RT info:eu-repo/semantics/article
T1 Simulation of hydrogen permeation through pure iron for trapping and surface phenomena characterisation
A1 Díaz Portugal, Andrés
A1 Zafra, A.
A1 Martínez Pañeda, Emilio
A1 Alegre Calderón, Jesús Manuel
A1 Belzunce, J.
A1 Cuesta Segura, Isidoro Iván
K1 Hydrogen embrittlement
K1 Hydrogen trapping
K1 Hydrogen permeation
K1 Finite Element modelling
K1 Resistencia de materiales
K1 Strength of materials
AB There is a need for numerical models capable of predicting local accumulation of hydrogen near stress concentrators and crack tips to prevent and mitigate hydrogen assisted fracture in steels. The experimental characterisation of trapping parameters in metals, which is required for an accurate simulation of hydrogen transport, is usually performed through the electropermeation test. In order to study grain size influence and grain boundary trapping during permeation, two modelling approaches are explored; a 1D Finite Element model including trap density and binding energy as input parameters and a polycrystalline model based on the assignment of a lower diffusivity and solubility to the grain boundaries. Samples of pure iron after two different heat treatments – 950 °C for 40 min and 1100 °C for 5 min – are tested applying three consecutive rising permeation steps and three decaying steps. Experimental results show that the finer grain microstructure promotes a diffusion delay due to grain boundary trapping. The usual methodology for the determination of trap densities and binding energies is revisited in which the limiting diluted and saturated cases are considered. To this purpose, apparent diffusivities are fitted including also the influence of boundary conditions and comparing results provided by the constant concentration with the constant flux assumption. Grain boundaries are characterised for pure iron with a binding energy between 37.8 and 39.9 kJ/mol and a low trap density but it is numerically demonstrated that saturated or diluted assumptions are not always verified, and a univocal determination of trapping parameters requires a broader range of charging conditions for permeation. The relationship between surface parameters, i.e. charging current, recombination current and surface concentrations, is also studied showing that trapping phenomena are stronger during the diluted steps and that recombination currents are much higher than the steady state obtained flux.
PB Elsevier
SN 0167-8442
YR 2020
FD 2020-12
LK http://hdl.handle.net/10259/5667
UL http://hdl.handle.net/10259/5667
LA eng
NO Ministry of Economy and Competitiveness of Spain through gran RTI2018-096070-B-C33. E. Martínez-Pañeda also acknowledges financial support from EPSRC funding under grant No. EP/R010161/1 and from the UKCRIC Coordination Node, EPSRC grant number EP/R017727/1, which funds UKCRIC’s ongoing coordination.
DS Repositorio Institucional de la Universidad de Burgos
RD 23-abr-2024