Hydrogen detection in high strength dual phase steel using scanning Kelvin probe technique coupled with XPS analyses of the surface oxidefilm

摘要

The sensitivity of high strength steel to hydrogen embrittlement is the main limitation to use thesegrades in automotive design. The scanning Kelvin probe (SKP) was proved to be relevanttechnique to study hydrogen distribution in steels. However, the mechanism that led to potentialdrop measured by SKP was still uncleared, but linked to surface evolutions under hydrogen flux.Thus, SKP measurements were coupled with X-ray photoelectron spectroscopy (XPS) analysesand electrochemical hydrogen investigations to study the modification of the native oxide layerunder hydrogen flux from the bulk in a high strength dual phase steel. The results showed that boththe Fe~(2+)/Fe~(3+) ratio and the -OH/-O_2 contributions in XPS were modified. Hydrogen reduces theoxide film that leads to Volta potential drop. Exposure in the air slowly re-oxidized the surface thatnobles Volta potential proportionally to amount of the surface Fe~(3+) species. Thus, measured Voltapotential is function of two processes oxide reduction and re-oxidation. Kinetic of surface oxidation- re-oxidation must be controlled and quantified to estimate hydrogen flux by SKP techniques. Afterthat SKP potential, calibrated using XPS data can be used for estimation of extremely lowhydrogen fluxes, which can be result of low efficiency corrosion processes.