Influence of minor alloying elements on the initial stages of oxidation of austenitic stainless steel materials

Surface oxidation of Fe‐19Cr‐17Ni, Fe‐19Cr‐18Ni‐1Al and TiC‐enriched Fe‐19Cr‐18Ni‐1Al alloys was investigated by photoelectron spectroscopy (PES). The experiments were conducted at 323 K in pure O₂ (2.7 × 10^?6 mbar). Composition and morphology of the nanoscale surface oxides were determined quantitatively by inelastic electron background analysis. Moreover, use of synchrotron radiation facilities were necessary to obtain improved sensitivity for studying minor alloying elements such as Al and Si. The results indicate oxygen‐induced segregation of Al, which significantly hinders the oxidation of the major alloying elements Fe and Cr. Ti remains in its inert carbide form. The relative concentration of Fe within the oxide layer was found to increase with the oxide‐layer thickness, indicating greater mobility of Fe relative to other alloying elements. Copyright © 2008 John Wiley & Sons, Ltd.     

A more general method for ranking the enrichment of alloying elements in passivation films

The corrosion of alloys is often characterized by an enrichment of one or other of the alloying elements within the surface oxide or even within the underlying metallic phase. For some three decades the measurement of such surface enrichment has been one of the most important contributions made by XPS to corrosion science. X‐ray photoelectron spectroscopy permits the composition of the oxide film to be distinguished from that of the metallic surface underlying the oxide so that both can be determined independently. In the mid‐1970s these measurements were crucial in showing that the selective enrichment of chromium in the electrochemical passivation of stainless steel occurred by selective dissolution of iron, and not by selective oxidation of chromium. Measurements of this type are important also in active corrosion, where there is no stable oxide film, as in studies of dealloying phenomena. The literature now contains numerous cases, many published by one of us (K.A.) based on studies of novel alloys produced in the Institute for Materials Research at Sendai. Typically, measurements are made for a series of binary compositions A_xB_y ranging from A‐rich to B‐rich alloys, in media that reflect the intended use of the alloy. The results are normally produced in the form of plots of cation composition Aⁿ⁺/(Aⁿ⁺ + B^m+) against bulk composition A/(A + B) or, in the case of dealloying, as A_surface/(A_surface + B_surface) against the bulk composition. Although graphical representation is useful in giving the full picture of the alloy's behaviour, it is not so useful in cataloguing or indexing performance. In this paper we suggest a means to give a rank or performance index as a single number that will characterize the behaviour of the alloy over a wide range of composition for a given medium or exposure condition. The rank number does not imply that any particular mechanism of enrichment is in operation; in various cases of corrosion it might occur by selective precipitation (FeOOH on steels, CuO on cupronickels), by selective dissolution (dezincification of brass) or by preferential incorporation of ions in a passivating oxide or oxyhydroxide (Cr³⁺ on stainless steels). Although the rank has no mechanistic implications, it is useful within a known class of mechanistic behaviour for indicating the magnitude of the effect and thus for enabling an XPS measurement to be indicative of wanted, or unwanted, behaviour. For example, the rank number could be useful in indicating, perhaps from a single alloy composition, whether a degree of passivation is likely to be achieved for that mix of metallic elements. Copyright © 2004 John Wiley & Sons, Ltd.     

Density functional theory study of ω phase in steel with varied alloying elements

The presence of a long-abandoned hexagonal omega (ω) phase in steel samples is recently gaining momentum owing to the advances in transmission electron microscopy (TEM) measurements, even though it is already reported in other transition-metal alloys. The stabilization of this metastable phase is mainly investigated in presence of C, even though the formation of the ω phase is attributed to the combined effect of many factors, one among which is the enrichment of solute elements such as Al, Mn, Si, C, and Cr in the nanometer-sized regimes. The present study investigates the effect of the above alloying elements in ω-Fe using density functional theory (DFT) calculations. It is seen that the magnetic states of the atoms play a major role in the stability of ω-Fe. Cohesive energy calculations show that the alloying elements affect the energetics and stabilization of ω-Fe. Further, density of states calculations reveal the variation in d-band occupancy in the presence of alloying elements, which in turn affects the cohesive energy. Phonon band structure calculations show that only ω-Fe with substitutional C shows positive frequencies and hence possess thermodynamic stability. Finally, we confirm the existence of ω-Fe using TEM measurements of a steel sample containing the same alloying elements. Our results can shed light on the stabilization of the ω in other transition-metal alloys as well, in the presence of minor alloying elements.     

Study of interface diffusion and reaction between Zr3N4 and stainless steel

The effect of annealing treatment on the interface diffusion and reaction between Zr₃N₄/stainless steel was studied by AES depth profiling along with line shape analysis. The Zr₃N₄ film was deposited on stainless‐steel substrates by reactive magnetron sputtering. Scanning electron microscopy, electron diffraction, AES and UV–VIS reflection were performed to characterize the deposited film. The results indicated that the interface diffusion between Zr₃N₄ and stainless steel took place during deposition and can be promoted by annealing treatment, but no interface reaction took place before or after annealing treatment. High‐temperature and long‐time annealing treatment resulted in obvious oxidation of the Zr₃N₄ layer. The UV–VIS reflection results indicated that the absorption band of Zr₃N₄ film shifted to shorter wavelength after annealing treatment. Copyright © 2003 John Wiley & Sons, Ltd.     

Evolution of surface chemistry during sintering of water-atomized iron and low-alloyed steel powder

Water-atomized iron and steel powder is commonly used as the base material for powder metallurgy (PM) of ferrous components. The powder surface chemistry is characterized by a thin surface oxide layer and more thermodynamically stable oxide particulates whose extent, distribution, and composition change during the sintering cycle due to a complex set of oxidation–reduction reactions. In this study, the surface chemistry of iron and steel powder was investigated by combined surface and thermal analysis. The progressive reduction of oxides was studied using model sintering cycles in hydrogen atmospheres in a thermogravimetric (TG) setup, with experiments ended at intermediate steps (500–1300°C) of the heating stage. The surface chemistry of the samples was then investigated by means of X-ray photoelectron spectroscopy (XPS) to reveal changes that occurred during heating. The results show that reduction of the surface oxide layer occurs at relatively lower temperature for the steel powder, attributed to an influence of chromium, which is supported by a strong increase in Cr content immediately after oxide layer reduction. The reduction of the stable oxide particulates was shifted to higher temperatures, reflecting their higher thermodynamic stability. A complementary vacuum annealing treatment at 800°C was performed in a furnace directly connected to the XPS instrument allowing for sample transfer in vacuum. The results showed that Fe oxides were completely reduced, with segregation and growth of Cr and Mn oxides on the particle surfaces. This underlines the sequential reduction of oxides during sintering that reflects the thermodynamic stability and availability of oxide-forming elements.     

EIS and XPS studies on passive film of AISI 304 stainless steel in dilute sulfuric acid solution

Electrochemical impedance spectroscopy and XPS studies on AISI 304 stainless steel in naturally aerated 0.5 M H₂SO₄ solution were carried out at room temperature. The valuable model of the metal/solution interphase was established, and the reliable equivalent electrical circuits in the solution were presented. The analysis of the chemical composition of passive film on AISI 304 stainless steel was carried out by XPS. The passive film of AISI 304 stainless steel is composed of oxyhydroxides, Fe₂O_3, FeO, Cr₂O₃, NiO, sulfate, sulfite, and sulfide (FeS, NiS). It is reported that the ferrous sulfide film formed on AISI 304 stainless steel in the dilute sulfuric acid solution. The possible process in which sulfuric acid is reduced to sulfite and sulfide is proposed. The galvanic interaction of sulfide inclusions with the base alloy is introduced. Copyright © 2011 John Wiley & Sons, Ltd.     

Exploring the relationship between the surface chemistry and the corrosion behavior of electropolymerized polypyrrole films deposited on the surgical ISO 5832-1 stainless steel

In the present work, electropolymerized polypyrrole (PPy) films were obtained on the surface of the surgical ISO 5832-1 stainless steel. The films were obtained from solutions containing 0.1M and 0.5M of the monomer by cyclic voltammetry deposition. The correlation between the surface chemistry of the as-deposited films and the corrosion behavior of the coated substrate is explored. X-ray photoelectron spectroscopy was used to study the chemical state of the main elements in the PPy films. Electrochemical impedance spectroscopy and potentiodynamic polarization tests were employed to evaluate the corrosion resistance of the PPy-coated samples. The tests were conducted in phosphate-buffered saline solution at 37°C. The measured corrosion current densities were dependent on the doping level of the PPy film and decreased with the reduction of the doping level of the PPy layer.     

Surface mobility and diffusion at interfaces of polystyrene in the vicinity of the glass transition

Symmetric polydisperse (M_w = 23 × 10⁴, M_w/M_n = 2.84) and monodisperse (M_w = 21 × 10⁴, M_w/M_n < 1.05) polystyrene (PS), and asymmetric polydisperse PS/poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) interfaces have been bonded in the vicinity of the glass transition temperature (T_g) of PS. In a lap-shear joint geometry, strength develops in all cases with time to the fourth power, which indicates that it is diffusion controlled. Strength developing at short times at the polydisperse PS/PS interface, at 90°C, is higher than that at the monodisperse interface, at 92°C (at T_g − 13°C in both cases), presumably due to the contribution of the low molecular weight species. The decrease of strength at the PS/PPO interface when the bonding temperature decreases from 113 to 70°C, i.e., from T_g + 10°C to T_g − 33°C of the bulk PS, indicates a high molecular mobility at the surface as compared to that in the bulk, and can be expressed by a classical diffusion equation, which is valid above T_g (of the surface layer). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 567–572, 1998     

Interface diffusion and chemical reaction of PZT layer/Si (111) sample during the annealing treatment in air

The interface diffusion and chemical reaction between a PZT (PbZrxTi1-xO3) layer and a Si(111) substrate during the annealing treatment in air have been studied by using XPS (X-Ray Photoelectron Spectroscopy) and AES (Auger Electron Spectroscopy). The results indicate that the Ti element in the PZT precursor reacted with residual carbon and silicon, diffused from the Si substrate, to form TiCx, TiSix species in the PZT layer during the thermal treatment. A great interface diffusion and chemical reaction took place on the interface of PZT Si also. The silicon atoms diffused from silicon substrate onto the surface of PZT layer. The oxygen atoms, which came from air, diffused into silicon substrate also and reacted with Si atoms to form a SiO2 interlayer between the PZT layer and the Si (111) substrate. The thickness of SiO2 interlayer was proportional to the square root of treatment time. The formation of the SiO2 interlayer was governed by the diffusion of oxygen in the PZT layer at low annealing tempera     

Distribution analysis of trace elements in low alloy steel by means of EPMA,SIMS, and TEM

A combination of chemical analysis, EPMA, SIMS, and TEM was applied to gain information on the bulk values, the microstructure and the microdistribution of contaminants. The limitations of classical chemical analysis were overcome by the application of highly sophisticated analytical techniques. Optimized measurement conditions were worked out for SIMS analysis and basic data such as relative sensitivity factors were gained for further investigations. A correlation between the microdistribution of contaminants and mechanical data could not be established so far, since only two samples were investigated.List of acronyms used BAS British Association of Standardisation (UK) - CGHE carrier gas hot extraction - DL detection limit - ED energy discrimination - EPMA electron probe micro analysis - E ₀ energy of primary ions - HMR high mass resolution - I _B primary ion beam current - NBS National Bureau of Standards (USA) - OES optical emission spectroscopy - PI primary ions - RSF relative sensitivity factor - SI secondary ions - SIMS secondary ion mass spectrometry - SKF SKF Analytica Taeby (Sweden) - TEM transmission electron microscopy - XRFA X-ray fluorescence analysis - d _A diameter of analyzed area     

A systematic determination of diffusion coefficients of trace elements in open and restricted diffusive layers used by the diffusive gradients in a thin film technique

A systematic comparison of the diffusion coefficients of cations (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and oxyanions (Al, As, Mo, Sb, V, W) in open (ODL) and restricted (RDL) diffusive layers used by the DGT technique was undertaken. Diffusion coefficients were measured using both the diffusion cell (D_cell) method at pH 4.00 and the DGT time-series (D_DGT) method at pH 4.01 and 7.04 (pH 8.30 was used instead of 7.04 for Al) using the Chelex-Metsorb mixed binding layer. The performance of Chelex-Metsorb as a new DGT binding layer for Al uptake was also evaluated for the first time. Reasonable agreement was observed between D_cell and D_DGT measurements for both ODL and RDL, except for V and W. The ratios of D_cell/D_DGT for V of 0.44 and 0.39, and for W of 0.66 and 0.63 with ODL and RDL respectively, were much lower due to the formation of a high proportion of polyoxometalate species at the higher concentrations required with the D_cell measurements. This is the first time that D values have been reported for several oxyanions using RDL. Except for Al at pH 8.30 with ODL, all D_DGT measurements were retarded relative to diffusion coefficients in water (D_W) for both diffusive hydrogels. Diffusion in RDL was further retarded compared with ODL, for all elements (0.66–0.78) with both methods. However, the degree of retardation observed changed for cations and anions at each pH. At pH 7.04 cations had a slightly higher D_DGT and oxyanions had a slightly lower D_DGT than at pH 4.01 for both ODL and RDL. It is proposed that this is due to partial formation of acrylic acid functional groups (pK_a ≈4.5), which would be fully deprotonated at pH 7.04 (negative) and mostly protonated at pH 4.01 (neutral). As Al changes from being cationic at pH 4.01 to anionic at pH 8.30 the results were more complex.     

Effects of pH and a hydrogenation stimulator on rate constants of cathodic evolution of hydrogen and its diffusion into steel in acid sulfate solutions

From steady-state and non-steady-state polarization measurements, kinetics parameters for the hydrogen evolution reaction at carbon steel in acid sulfate solutions in the absence and in the presence of KCNS are calculated. Based on the results obtained by an electrochemical diffusion method and using the Iyer-Pickering-Zamanzadeh analysis, apparent rate constants for the principal stages of the hydrogen evolution reaction are calculated.     

Ennoblement of stainless steel in the presence of glucose oxidase: nature and role of interfacial processes

The ennoblement of the free corrosion potential (E(corr)) of AISI 316L stainless steel which did not occur in synthetic fresh water (SFW), was observed after introduction of glucose oxidase (Gox) and glucose, or of hydrogen peroxide (H(2)O(2)). The composition of the surface was monitored using AFM and XPS, a detailed XPS analysis being based on the discrimination between oxygen of organic and inorganic nature proposed in a previous study. In H(2)O(2) medium, the main changes regarding the inorganic phase were the increase of the oxygen concentration in the passive film, the increase of the molar concentration ratio of oxidized species Fe(ox)/Cr(ox) and the growth of nanoparticles, presumably made of ferric oxide/hydroxide. In Gox medium, no significant changes were observed in both oxygen concentration and Fe(ox)/Cr(ox) ratio, but the density of colloidal particles decreased, indicating a dissolution of Fe oxide/hydroxide under the influence of gluconate. In contrast with H(2)O(2), in SFW and Gox the amount of organic compounds increased due to the accumulation of polysaccharides and proteins. The influence of glucose oxidase on the ennoblement of stainless steel is not due to indirect effects of H(2)O(2) through the change of surface composition. The E(corr) ennoblement seems to be directly due to the presence of H(2)O(2) and to the electrochemical behavior of H(2)O(2) and related oxygen species. This consideration is important for understanding and controlling microbial influenced corrosion.     

Determination of some trace elements in high-purity aluminium, zinc and commercial steel by AAS after preconcentration on amberlite XAD-1180 resin

The determination of trace metals, e.g. Bi, Cd, Pb, in high-purity aluminium, zinc and commercial steel by flame or graphite furnace atomic absorption spectrometry following their preconcentrations as iodo complexes on XAD-1180 resin by means of a short column system is described. The recoveries are quantitative (95%). The relative standard deviations varies between 6% and 10%. The relative errors are less than 8% in a concentration range of 1 × 10^–3 –4 × 10^–5%. Detection limits for flame AAS and GFAAS were in the ranges of 0.002–0.110 g/ml and 0.0003–0.004 g/ml or in the ranges of 0.08–4.40 g/g and 0.012–0.16 g/g with respect to the solid samples, respectively.