Hydrogen‐damaged defects near the surface in heavily deformed iron and steels investigated by slow positron annihilation spectroscopy

Abstract

Hydrogen-damaged defects of heavily deformed iron, AISI 304-, and 316-stainless steels were investigated by measuring Doppler broadening energy spectra (DBES) of positron annihilation radiation. It is interestingly found that S-parameter as a function of energy on three kinds of deformed samples falls into the similar variation, independent of chemical elements and impurities. A larger S value near the surface in deformed and hydrogen-damaged samples than in samples without hydrogen-damaged samples is because of the additional larger-sized defects (e.g. voids) induced due to hydrogen damage.1 Introduction Positron annihilation spectroscopy (PAS) has been widely used as a probe for the determination of defects at the atomic level in solids, including vacancies, vacancy clusters, dislocations, and nanometer-scale voids [1]. The use of variable mono-energy positron beams allows one to determine the depth profile of defects in solids, and is particularly suitable for analysis of surface and near-surface defects [2]. Hydrogen damage or hydrogen embrittlement (HE) of iron and steels has been investigated by PAS methods for many years.The effect of hydrogen and helium on microvoid formation in iron and nickel has been studied by positron annihilation lifetime (PAL) and coincidence Doppler broadening (CDB) [3]. Takagi et al. [4] reported PAL measurement by slow positron beam in iron films, hydrogeninduced vacancies were grown under different hydrogen pressures. Cizek et al.[5] studied hydrogeninduced defects in bulk niobium by XRD and PAS, and they indicated that vacancy-hydrogen complexes were introduced into the samples due to hydrogen loading. Recently, Wu et al. [6][7][8] studied hydrogeninduced defects and hydrogen damage by PAL and slow positron beam in annealed AISI 304 and 316 stainless steels, and indicated that hydrogen damage starting from surface to the bulk had a significant difference with depth, and strongly depends on the condition of hydrogen-charging. In this paper, we further report hydrogen-damaged defects of heavily deformed iron, AISI 304-, and 316-stainless steels by measuring Doppler broadening energy spectra (DBES) of positron annihilation radiation. The type of hydrogen-damaged defects near the surface on three kinds of deformed samples is discussed.

Characterization of proton irradiation-induced defect in the A508-3 steel by slow positron beam

“…It also can be seen that at a dose of 7.60 Â 10 17 ions/cm 2 , more open-volume defects or larger defects were detected than at a dose of 1.52 Â 10 17 and 3.04 Â 10 17 ions/cm 2 . The values of effective diffusion length (L +,1 ) are comparable with the reported values (43 nm for hard iron, 78 nm for 304, 59 nm for 316 steels) by Wu and Jean [3].…”

“…Positron-annihilation spectroscopy (PAS) is one of the powerful and well-established techniques for characterizing vacancy-type defects (microvoids and open volume regions) of materials [3]. Doppler broadening spectroscopy (DBS) of the mono-energetic positron beam allows a measurement of defect profiles [4,5].…”

Estimate of the Crystallite Size for Nanocrystalline AISI 316L Stainless Steel and Armco Iron Processed by Hydrostatic Extrusion Using Variable Energy Positron Beam

“…Higher values for the S-parameter saturation can be associated with increased concentration of defects. The positron diffusion length L + obtained for the reference sample was 79.4 ± 1.0 nm, which corresponds to the values presented in the literature [23]. For the samples 71 and 72 of the AISI 316L steel L + was equal to 3.3±0.4 nm and 13.4±2.0 nm, respectively.…”

Positron beam and RBS studies of thermally grown oxide films on stainless steel grade 304

“…Qiang-mao et al [28] evaluated L + in A 508-3 steel on the level of 100 nm. Wu and Jean [29] found that the thickness of the oxide film for 304 and 316 stainless steels is 20 nm and 5 nm and positron diffusion length is 11 nm and 5 nm, respectively. Positron diffusion length in the bulk for 304 and 316 steels was found to be 78 nm and 59 nm.…”