Surface Oxidation Of Alloys Research Articles

Prediction of the catalytic mechanism of hydrogen evolution reaction enhanced by surface oxidation on FCC_CoCrFeNi and Co0.35Cr0.15Fe0.2Mo0.1Ni0.2 multi-principal element alloys based on site preference

Some multi-principal element alloy (MPEA) catalysts may exhibit the ability to promote the hydrogen evolution reaction (HER) and maintain stability under acidic conditions. Here, we investigated the impact of ordered behavior and surface oxidation of FCC_CoCrFeNi and Co0.35Cr0.15Fe0.2Mo0.1Ni0.2 MPEAs on HER performance through first-principles calculations. The ordering behaviors of MPEAs were described using L12_AuCu3 sublattice model and the predicted site occupying fractions (SOFs). And we found that the catalytic activity of single intermediate *H at top or bridge adsorption sites surpassed that at the hollow site. However, the hollow site exhibits strong adsorption towards *H, resulting in the transfer of *H from other sites to hollow site. Meanwhile, compared to those containing only hydrogen, MPEAs with both hydrogen and oxygen exhibit lower overpotentials, primarily due to oxygen facilitating hydrogen adsorption and subsequent desorption from MPEA surfaces, thus, such fundamental finding highlights the beneficial role of alloy surface oxidation in promoting HER performance. Furthermore, the overpotential values of the three slab models based on SOFs are similar, demonstrating considerably consistent atomic distribution behaviors, thereby better reflecting the overall catalytic performance of ordered MPEAs. These explorations bring new insights into the ordered behavior and surface oxidation of MPEAs in HER catalysis.

Oxidative Corrosion Mechanism of Ti2AlNb-Based Alloys during Alternate High Temperature-Salt Spray Exposure

This study investigates the corrosion damage mechanisms of Ti2AlNb-based alloys under high temperature, salt spray and coupled high temperature-salt spray conditions. This alloy was analysed in detail from macroscopic to microscopic by means of microscale detection (XRD, SEM and EDS). The results indicated that Ti2AlNb-based alloy surface oxide layer is dense and complete, and the thickness is only 3 µm after oxidation at 650 °C for 400 h. Compared to the original sample, the production of the passivation film resulted in almost no damage to Ti2AlNb-based alloy after 50 cycles of salt spray testing at room temperature. The tests showed that Ti2AlNb alloy shows good erosion resistance at 650 °C and in salt spray. However, this alloy had an oxide layer thickness of up to 30 µm and obvious corrosion pits on the surface after 50 cycles of corrosion under alternating high temperature-salt spray conditions. The Cl2 produced by the mixed salt eutectic reaction acted as a catalytic carrier to accelerate the volatilisation of the chloride inside the oxide layer and the re-oxidation of the substrate. In addition, the growth of unprotected corrosion products (Na2TiO3, NaNbO3 and AlNbO4) altered the internal structure of the oxide layer, destroying the surface densification and causing severe damage to the alloy surface.

Elevated temperature nanoscratch of Inconel 617 Superalloy

Inconel 617 superalloy is a main candidate to be used for mechanical and tribo-components in high temperature helium-cooled reactors. Recent findings show that it grows a unique surface oxide, especially under high temperature helium with distinct wear, friction, and contact properties. This study reports the elevated temperature nanoscratch behavior of Inconel 617 and further utilizes it to understand the effect of temperature on contact friction constituent contributors, adhesion and plowing at small scales. Inconel 617 is aged in high temperature helium, and consequently, the total kinetic friction coefficient of the alloy surface oxide is obtained in temperatures ranging from 25 °C to 400 °C. A finite element model is developed and validated based on the experimental results. The model is then utilized along with previously established techniques to determine the adhesion and plowing components of the friction coefficient. At small scale, the experimental results show that with increasing temperature the friction coefficient increases. It was inferred that this increase is mainly due to the increased contribution of plowing friction at high levels of deformation.

XPS Analysis of Oxide Formed on the Surface of Co-28Cr-6Mo-1Si Alloy Oxidized at 550°C

This work investigated the influence of oxidation durations on the formation of oxide on the surface of wrought Co-28Cr-6Mo-1Si alloy. The iso-thermal oxidation was individually performed in air at 550°C for 4, 12 and 24 h. For comparison, the surface of the non-oxidized Co-28Cr-6Mo-1Si alloy was concurrently examined. The chemical compositions of the non-oxidized and oxidized alloys were principally analyzed via X-ray photoelectron spectroscopy (XPS). The XPS results revealed that the surface of the non-oxidized alloy enriched in Cr-oxide. After oxidation treatment, the Co-oxide, existing as Co2+ state was observed coexisting with two Cr-oxide states, Cr3+ and Cr4+. The low concentrations of Mo6+ were also observed on the oxidized alloy surface. With the increase in oxidation durations, the Co-oxide was suppressed by Cr-oxide. The XPS depth profile analysis indicated that the thickness of the oxide film increased with increasing the oxidation duration.

Evaluation of Electrode Degradation and Projection Weld Strength in the Joining of Steel Nuts to Galvanized Advanced High Strength Steel

Abstract Projection welding of steel weld nuts to advanced high strength steel (AHSS) in automotive applications allows for the reliable mounting of critical components with different thicknesses to the vehicle body. However, the galvanized coatings commonly used on AHSS result in electrode surface degradation during welding. In this study, the electrode degradation and its effect on the mechanical properties of welded steel nuts and AHSS sheets are investigated. Two common electrode materials are tungsten/copper and beryllium-free class III copper—both display the formation of an oxidized alloy surface layer and pitting as weld number increases. Unlike resistance spot welding, where electrodes grow in the contact area diameter as they degrade, projection welding electrodes do not experience this type of mechanical degradation. Instead, increased resistance at the electrode interface with increasing weld number results in higher temperatures at the weld interface and a larger fusion zone size, which is responsible for an observed 30% increase in weld strength over the span of 10,000 welds.

Phosphonic acid functionalization of nanostructured Ni–W coatings on steel

Abstract The functionalization of nanocrystalline Ni–W coatings, formed by galvanostatic pulsed electrodeposition on steel, by thermal treatment of octadecylphosphonic acid self-assembled on the oxidized alloy surface is studied by Raman spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy, AFM and electrochemical techniques. Results show that this procedure preserves the surface topography and the optimum mechanical properties of the alloy. More importantly, it turns the alloy surface highly hydrophobic and markedly improves its corrosion resistance, in particular to pitting corrosion in aggressive solutions containing chloride anions. The ability of the phosphonate layer to improve surface properties arises from the barrier properties introduced by the hydrocarbon chains and the strong bonds between the phosphonate head and the underlying surface oxides.

Low-temperature and instantaneous high-rate output performance of AB5-type hydrogen storage alloy with duplex surface hot-alkali treatment

The excellent low-temperature and instantaneous high-rate output performance of MmNi3.7Co0.7Mn0.3Al0.3 alloy are obtained via hot-alkali treatment (K alloy) and duplex hot-alkali treatments with reducing agents, including N2H4 (KN alloy), NaH2PO2 (KP alloy) and NaBH4 (KB alloy). The charge transfer process on the alloy surface is the primary control step that influences the electrochemical properties at −40 °C. Scanning electron microscopy and energy dispersive X-ray analyses demonstrate that a high electrocatalytic Ni-and Co-rich layer is formed via the preferential dissolution of Al and Mn and that the alloy surface oxide is effectively removed via the duplex surface hot-alkali treatments. Thus, the charge-transfer resistance decreases and the exchange current density increases obviously in the treated alloys, making the K, KN, KP and KB alloys exhibit better activation property, high-rate dischargeability and instantaneous high-rate output performance at 20 °C, as well as higher discharge capacity, low-temperature dischargeability and high-power delivery at −40 °C. Based on the overall electrochemical properties of the alloys at various temperatures, a duplex surface modification of the hot-alkali treatment with NaH2PO2 is determined to be the best.

MECHANICAL AND TRIBOLOGICAL PROPERTIES OF OXIDE LAYERS OBTAINED ON Ti-6Al-7Nb ALLOY

The research presented in the paper was focused on determining the effects of thermal oxidation parameters on the mechanical and tribological properties of oxide layers formed on Ti-6Al-7Nb titanium alloy for biomedical applications. Titanium alloy was oxidized at 600 and 700°C for 72h. The study found that, at lower temperatures, the oxidized alloy surface was covered by a nonuniform oxide layer. A 100°C increase in the treatment temperature yielded a uniform layer covering the whole surface of the alloy. Hardness measurements showed that thermal oxidation resulted in the formation of oxide layers characterized by a 3-fold higher hardness compared to untreated alloy. Tribological tests showed that thermal oxidation effectively improves the resistance of Ti-6Al-7Nb alloy to sliding wear. Tribological tests demonstrated that an increased oxidation temperature was associated with improved resistance to sliding wear.

Surface oxidation of Alloy 617 in low oxygen partial pressure He–CO–CO2 environments at 750–850 °C

Surface Cr oxidation mechanism of Alloy 617 was investigated in He–CO–CO2 environments with PCO/PCO2 of either 9 or 1320 at temperatures 750–850°C. The activation energy for surface oxidation was 169.0±13.2kJ/mol in He–PCO/PCO2=9 and 234.4±8.9kJ/mol in He–PCO/PCO2=1320. The ambient oxygen partial pressure dependence of the measured oxidation rates was consistent with n-type behavior of Cr2O3, in which Cr interstitials are the primary mobile species. The oxidation rates measured were greater than that can be sustained only by lattice diffusion of Cr in Cr2O3, indicating that grain boundary diffusion of Cr plays a role in the Cr2O3 growth kinetics.

Characterization and electrochemical behavior of Pd-rich Pd-Ru alloys

Thin layers (0.1–5μm) of Pd-rich Pd-Ru alloys were prepared by potentiostatic electodeposition from baths containing aqueous solutions of RuCl3 and PdCl2 with HCl. Alloy bulk compositions were determined by atomic emission spectroscopy and energy dispersive analysis of X-rays. The crystal structure of the deposits was examined by X-ray diffraction. Alloy surface morphology was characterized by scanning electron microscopy and atomic force microscopy. Surface compositions were determined by X-ray photoelectron spectroscopy. General electrochemical behavior of Pd-Ru deposits was investigated using cyclic voltammetry. The processes of alloy surface oxidation and hydrogen adsorption/absorption were studied in 0.5M H2SO4 solutions at 298K. It was found that homogeneous fcc alloys were formed by Pd and Ru with the lattice parameter smaller than that of pure Pd.

Effects of H<sub>2</sub>O<sub>2</sub> on Characteristics of Films Formed on Surface of Ti6Al4V in Electrolyte by Micro-Arc Oxidation

Using micro-arc oxidation technology in preparation Ti6Al4V alloy surface oxidation film, adding to the electrolyte H2O2, influence of H2O2 addition amount of oxidation film characteristics has been studied. The results show that, H2O2 addition amount of 4.0 g·L-1, positive critical arcs voltage minimum, for 338 V. SEM analysis showed that, electrolyte of H2O2 addition amount by 1.0 g·L-1 increased to 4.0 g·L-1, film hole diameter after decreasing, micro-arc oxidation film layer of density increases. Oxidation film surface roughness reduced to 7.619 when H2O2 addition amount for 4 g·L-1. With H2O2 addition amount from 1.0 g·L-1 increased to 4.0 g·L-1, micro-arc oxidation film in the wear process mass loss is reduced, wear resistance for promotion.

Titanium alloy surface oxide modulates the conformation of adsorbed fibronectin to enhance its binding to α5β1 integrins in osteoblasts

Our laboratory has previously demonstrated that heat (600°C) or radiofrequency plasma glow discharge (RFGD) pretreatment of a titanium alloy (Ti6Al4V) increased the net negative charge of the alloy's surface oxide and the attachment of osteoblastic cells to adsorbed fibronectin. The purpose of the current study was to investigate the biological mechanism by which these surface pretreatments enhance the capacity of fibronectin to stimulate osteoblastic cell attachment. Each pretreatment was found to increase the binding (measured by ELISA) of a monoclonal anti-fibronectin Ig to the central integrin-binding domain of adsorbed fibronectin, and to increase the antibody's inhibition of osteogenic cell attachment (measured by hexosaminidase assay). Pretreatments also increased the binding (measured by ELISA) of anti-integrin IgG's to the α(5) and β(1) integrin subunits that became attached to fibronectin during cell incubation. These findings suggest that negatively charged surface oxides of Ti6Al4V cause conformational changes in fibronectin that increase the availability of its integrin-binding domain to α(5) β(1) integrins.

Effect of Oxide Growth Strain in Residual Stresses for the Deflection Test of Single Surface Oxidation of Alloys

Residual stresses developed in FeCrAlY and Ni80Cr20 alloys have been predicted considering growth strain and creep strain in oxide layer and creep strain in alloy or metal. Such stresses, a net compressive stress developed in oxide scales and a net tensile stress developed in alloy strip, produce deflection of a single surface oxidized specimen during high temperature isothermal oxidation. Stresses generated in these alloys and oxide scales were compared with creep deflections. Introducing oxide growth strain in the oxide scales increase the oxide stress value during the initial oxidation stage, during which creep analysis lacks prediction. Oxide stress reaches maximum value at certain oxidation time in the initial oxidation stage. After that oxidation time relaxation of oxide stress occurs considerably in later oxidation stage.

Development of New Alloys for SOFC Interconnects with Excellent Oxidation Resistance and Reduced Cr-Evaporation

Recently, metallic materials, especially Fe-Cr ferritic alloys (ex. ZMG232L), are promising as interconnect materials of solid oxide fuel cells (SOFCs) operated at around medium temperatures such as 700 - 850oC. As for these alloys, good oxidation resistance and good electrical conductivity in thin sheets are required. Moreover, it is needed to reduce Cr evaporation, which causes the degradation of the cell, from oxidized alloy surface. In this study, the effect of chemical compositions on required properties at elevated temperature was investigated and new alloys for SOFC Interconnects were developed.

Effect of Mn–Co spinel coating for Fe–Cr ferritic alloys ZMG232L and 232J3 for solid oxide fuel cell interconnects on oxidation behavior and Cr-evaporation

Metallic materials, especially Fe–Cr ferritic alloys, are promising as interconnect materials of solid oxide fuel cells (SOFCs) operated at around medium temperatures. ZMG232L is one of the developed Fe–Cr ferritic alloys for SOFC metallic interconnects. These metallic materials are usually machined or pressed into various shapes of interconnect parts, and thickness of these parts is often thin. However, the oxidation rate of thin sheet was much higher than that of thick one because Cr content decreased under oxide layer of edge part of thin sheet. Such accelerated oxidation behavior could be improved by reducing Mn, increasing Cr, and adding W in ZMG232L. It is also very important to reduce Cr-evaporation from the oxidized surface of ferritic alloys in cathode side. The aim of this study is to reduce the Cr-evaporation from oxidized alloy surface in air by coating with Mn–Co spinel oxide. In this study, oxidation behavior and Cr-evaporation of ZMG232L and improved Fe–Cr alloy, 232J3, coated with Mn–Co spinel oxide were investigated at elevated temperature in air. MnCo 2O 4 spinel coating on the pre-oxidized Fe–Cr ferritic alloy surface improved oxidation resistance and Cr-evaporation.

Surface oxide net charge of a titanium alloy: Comparison between effects of treatment with heat or radiofrequency plasma glow discharge

In the current study, we have compared the effects of heat and radiofrequency plasma glow discharge (RFGD) treatment of a Ti6Al4V alloy on the physico-chemical properties of the alloy's surface oxide. Titanium alloy (Ti6Al4V) disks were passivated alone, heated to 600 °C, or RFGD plasma treated in pure oxygen. RFGD treatment did not alter the roughness, topography, elemental composition or thickness of the alloy's surface oxide layer. In contrast, heat treatment altered oxide topography by creating a pattern of oxide elevations approximately 50–100 nm in diameter. These nanostructures exhibited a three-fold increase in roughness compared to untreated surfaces when RMS roughness was calculated after applying a spatial high-pass filter with a 200 nm-cutoff wavelength. Heat treatment also produced a surface enrichment in aluminum and vanadium oxides. Both RFGD and heat treatment produced similar increases in oxide wettability. Atomic force microscopy (AFM) measurements of metal surface oxide net charge signified by a long-range force of attraction to or repulsion from a (negatively charged) silicon nitride AFM probe were also obtained for all three experimental groups. Force measurements showed that the RFGD-treated Ti6Al4V samples demonstrated a higher net positive surface charge at pH values below 6 and a higher net negative surface charge at physiological pH (pH values between 7 and 8) compared to control and heat-treated samples. These findings suggest that RFGD treatment of metallic implant materials can be used to study the role of negatively charged surface oxide functional groups in protein bioactivity, osteogenic cell behavior and osseointegration independently of oxide topography.

Surface oxide net charge of a titanium alloy: Modulation of fibronectin-activated attachment and spreading of osteogenic cells

In the current study, we have altered the surface oxide properties of a Ti6Al4V alloy using heat treatment or radiofrequency glow discharge (RFGD) in order to evaluate the relationship between the physico-chemical and biological properties of the alloy's surface oxide. The effects of surface pretreatments on the attachment of cells from two osteogenic cell lines (MG63 and MC3T3) and a mesenchymal stem cell line (C3H10T1/2) to fibronectin adsorbed to the alloy were measured. Both heat and RFGD pretreatments produced a several-fold increase in the number of cells that attached to fibronectin adsorbed to the alloy at a range of coating concentrations (0.001–10 nM FN) for each cell line tested. An antibody (HFN7.1) directed against the central integrin binding domain of fibronectin produced a 65–70% inhibition of cell attachment to fibronectin-coated disks, indicating that cell attachment to the metal discs was dependent on fibronectin binding to cell integrin receptors. Both treatments also accelerated the cell spreading response manifested by extensive flattening and an increase in mean cellular area. The treatment-induced increases in the cell attachment activity of adsorbed fibronectin were correlated with previously demonstrated increases in Ti6Al4V oxide negative net surface charge at physiological pH produced by both heat and RFGD pretreatments. Since neither treatment increased the adsorption mass of fibronectin, these findings suggest that negatively charged surface oxide functional groups in Ti6Al4V can modulate fibronectin's integrin receptor activity by altering the adsorbed protein's conformation. Our results further suggest that negatively charged functional groups in the surface oxide can play a prominent role in the osseointegration of metallic implant materials.

A multiscale modelling study of Ni–Cr crack tip initial stage oxidation at different stress intensities

In this study, different scale analyses have been performed to understand the very beginning stage of the Ni–Cr(1 1 1) binary alloy surface oxidation mechanism. The finite elements method (FEM) has been applied to find the stress intensity effect on a compact tension (CT) specimen crack tip, and a 2-μm rectangular region has been prepared for the quasi-continuum (QC) model. The displacement load calculated by FEM was applied at the upper and lower boundaries of the QC model. The obtained atomic positions of the deformed crystal structure were considered for quantum chemical molecular dynamics (QCMD) analysis by placing water molecules on the surface. Water molecules dissociate on the top site followed by the quick diffusion of hydrogen atoms on the surface through the hollow sites. Hydrogen is easily transported into the lattice due to its small atomic size. Increases in stress intensity factor ( K) act to deform the structure, which augments oxygen penetration and reduces hydrogen diffusion time; as a consequence, changes in K result in an increase of metallic surface oxidation. Oxygen preferentially bonds with chromium to develop a protective passive film on the surface, and the quickly diffused hydrogen is trapped on the metal surface. Hydrogen bonds with the metal by receiving electrons and, therefore, works as an oxidant on the surface and weakens the metal atomic bond at the primary stage. Initially, the oxidized surface forms a strong bond with oxygen, resulting in the breakage of metal–metal bonds. Therefore, this hydrogen action enhances the very early stage surface oxidation.

Dissimilar Joining of Aluminum Alloy and Steel by Resistance Spot Welding

Recently, there are strong demands for light-weight, fuel efficient cars. An effective joining technique to join light metals, such as Al and Mg alloys, with steel is required. Mg alloy and steel are especially difficult pair of metals to join. Due to not only Mg alloy's surface oxide, but also their complete phase separation nature, Mg alloy and steel do not form an intermetallic at the joint interface. We aimed to join Mg alloy and steel by using Mg-Zn eutectic reaction, Zn layer was inserted between Mg alloy and steel as plating on steel. A conventional resistance spot welding machine was used, and joint strength was evaluated by tensile strength tests. It was found that Mg alloy surface oxide are removed along with eutectic melt at low temperature, and at the same time, thin and uniform intermetallic layer of Fe-Al and Al-Mg were formed at the joint interface.

Electrochemical assisted deposition of calcium phosphate coatings for orthopaedic applications

Calcium phosphate (CP) coatings on Ti6Al4V alloy were grown at controlled current densities (from 3 to 10 mA cm−2) during electrochemical deposition (ECD). The thickness, structure and composition of the coatings were investigated by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results showed that the thickness (ranging from 3 to 16 μm) shows a parabolic increase with the applied deposition current density. The hexagonal hydroxyapatite (HA) structure was the main phase at the current density of 10 mA cm−2 during ECD. The potential–time curves showed that the CP deposition progresses due to the initial reduction of alloy surface oxide layer, after which a reduction of nitrate ions takes place on the active free surface sites. The kinetics of this process is enhanced by sufficiently high current densities. Such current densities have a direct influence on the local pH of the solution and determine the morphology, structure and composition of ECD products.