Oxidation Of Alloys Research Articles

Improvement of oxidation resistance and alumina regrowth ability of Ni-30Cr-5Al alloy without and with Y: Nanocrystallization effect

Nanocrystallization of Ni-Cr-Al alloys decreases critical Al content (NAl*) for Al2O3 scale formation down to a level much lower than practical alloy Al content (NAl), and this is particularly prominent for the alloys with NAl≤ NAl*. In this work, oxidation of coarse-grained (CG) Ni-30Cr-5Al with NAl > NAl* and its nanocrystalline (NC) counterpart has been studied, with the focuses on the following issues: (i) nanocrystallization effect on Al2O3 steady-state growth and regrowth; (ii) nanograin growth effect on Al2O3 adhesion; and (iii) role of Y played in NC alloys by comparing the differences in oxidation of the NC alloys without and with Y.

Plasma Electrolytic Oxidation of AZ31 Mg Alloy in Bipolar Pulse Mode and Influence of Corrosion to Surface Morphology of Obtained Coatings

The plasma electrolytic oxidation method was used with AZ31 magnesium alloy plates for improving the corrosion resistance of the alloy. Process parameters for the plasma electrolytic oxidation setup were optimized by studying the effects of KOH concentration, operating voltage, and pulse properties on the obtained coating. These conditions were then used to produce plasma electrolytic oxidation coated AZ31 sample and were tested by immersion in 3 % NaCl solution for 1 week. Three types of modifiers were used in the electrolyte and concentrations of the modifiers were varied to study the effect of concentration on the performance of coating obtained. The extent of corrosion was visually examined, and it was found that an electrolyte recipe with all three modifiers produced the best results.

Exploiting synergistic interaction in Cu-Zn-Ni alloy oxide films prepared by one-step anodizing for a highly sensitive non-enzymatic glucose sensor

A highly sensitive and precise electrochemical biosensor for glucose detection was developed by coupling synergetic catalysis of Cu-Zn-Ni oxide films. To enhance the catalytic performance of alloy, potentials between −0.5 V and 1.5 V are selected for potentiostatic oxidation. Notably, the oxidation process reveals the influence of Cl− in the electrolyte, leading to electrode surface etching, with increasing etching and grain boundary collapse at higher potentials. The electrochemical performance of the electrode was comprehensively evaluated using cyclic voltammetry (CV) and amperometric response in alkaline conditions. The catalytic electrode has an impressive linear response in the concentration range of 0.1 ∼ 1.0 mM glucose, with a sensitivity of 3775.11 μA·mM−1. Furthermore, the electrode exhibits remarkable stability and anti-interference properties, rendering it suitable for non-enzymatic glucose sensing applications.

Energy-release behavior of TiZrNbV high-entropy alloy

To further explore the potential of high-entropy alloys (HEAs) as energetic structural materials (ESMs) and promote development of HEA-ESMs, the energy-release behavior of TiZrNbV HEA with good mechanical properties and energy-releasing characteristics is investigated in this work. The analyses for the size, morphology and lattice structure of collected fragments as well as the appearance of penetrated target plate reveal that the serious deformation and adiabatic temperature rise of TiZrNbV HEA result in the target plate smelting, alloy crushing, component segregation, oxidation reaction and energy releasing. The alloy crushing, oxidation reaction and energy releasing behaviors all are directly decided by the penetrating velocity. With increasing penetrating velocity, the impact kinetic energy and adiabatic temperature rise enhances, then the fragment with the smaller size increases, the surface for the oxidation reaction increases, finally the releasing energy increases. Semi-quantitatively calculation demonstrates that increasing the crushing efficiency, especially the ratio of the fragments with the size of <100 μm can effectively increase the energy release rate of TiZrNbV HEA.

Effect of Fe on the oxidation, sulfidation and carburization behaviors of alloys in CO2 containing SO2

The effect of Fe on the oxidation, sulfidation and carburization behaviors of alloys in CO2 containing SO2 at 1000 ℃ was investigated using multiple evaluation methods, including first-principles, molecular dynamics simulation, high-temperature corrosion experiment and thermodynamic analysis. The adsorption capacity of both gas molecules on FeCr alloy surface was stronger than that on NiCr alloy surface. The molar content of O, C and S atoms in Fe-25Ni-22Cr alloy was higher than that in Ni-25Fe-22Cr alloy. The increase of Fe content promoted the reactions between alloy elements and O, C, S atoms, which caused serious corrosion of Fe-Ni-Cr alloys.

Anode behavior and oxidation of Zn22Al alloy doped with scandium

The article contains the results of potentiodynamic and thermogravimetric research of anode behavior and oxidation of Zn22Al alloy, doped with scandium, in various media. The anode, kinetic and energy characteristics of alloys in isothermal conditions have been established. Doping of the Zn22Al alloy with scandium in an amount of 0.1 to 1.0 wt. % contributes to the increase of its anodic resistance to oxidation. The rate of oxidation and corrosion of alloys doped (0.01–0.1%) with scandium is 1.5–3 times lower than that of the Zn22Al alloy. Alloy oxidation products consist of a mixture of protective films ZnO, Sc2O3, ZnAl2O4 and Al2O3·Sc2O3.

Simulation of high-temperature zirconium alloy oxidation in a nitrogen, oxygen and steam mixture

The paper presents a correlation model of high-temperature zirconium alloy oxidation in a mixture of gases (steam, nitrogen and oxygen) for the weight gain calculation of the oxidized sample. The essence of the model consists in using the linear interpolation between the kinetic constants of oxidation in pure gases to describe the oxidation kinetics in gas mixtures. The approach allows one to describe the oxygen weight gain with different contents of gases in steam, nitrogen and oxygen mixtures. The model was validated against experimental data on oxidation in an air-steam mixture in a proportion of 50% to 50% of the volume. For temperatures of 1200 °C and 1400 °C, prior to the 625th second, the deviation between the experimental data and the simulation results is not more than 18%; for 800 °C, prior to the 14th hour, the deviation between the experimental data and the simulation results is not more than 40%. Besides the air-steam mixture, the paper presents the results of the weight gain calculation using the proposed model for oxidation in an oxygen-nitrogen mixture and in a steam-oxygen mixture at 800 °C and 1400 °C.

Oxidation of TiAl alloy by oxygen grain boundary diffusion

Ti–Al intermetallic alloys have a number of advantages for the manufacture of aviation and car details. The use of these alloys is limited by their oxidation at high temperatures, which is associated with structural features and the presence of micro and nanosized grains. In such materials, grain boundary diffusion of oxygen can be active, which contributes to the acceleration of oxidation upon heating. In this paper, we present a two-dimensional model for research the diffusion which is accompanied by oxidation. The structure of TiAl is specified as symmetrically alternating grains with a clear separation of boundaries and triple junctions between them. Diffusion and chemical properties of grains and boundaries are different. The problem is formulated in a two-dimensional formulation and solved numerically. The influence of changes in the composition over time on the penetration of oxygen is taken into account. For the convenience of numerical research and analysis of the results, dimensionless variables are used. To solve the diffusion equation, an implicit difference scheme of splitting in coordinates is used. The equations of chemical kinetics are solved using an algorithm similar to the implicit Euler method using an iterative procedure. The results demonstrate the influence of different variants of kinetic regimes on the concentration distribution and integral concentrations of reagents and oxides.

Impact of thermal oxidation parameters on micro-hardness and hot corrosion of Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr alloy

Protective oxide layers on Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr (TC21) alloy with equiaxed microstructure considerably influence micro-hardness and hot corrosion resistance. The present work’s thermal oxidation of TC21 alloy was performed at 600, 700, and 800 °C for 5, 20, and 50 h durations. Hot corrosion methods in NaCl and NaCl + Na2SO4 salt media were applied to raw (unoxidized) and oxidized samples at 600 and 800 °C for 50 h. Hot corrosion was conducted at 600 °C for 5 cycles with 10-h steps. The best oxide layer thickness was observed at 800 °C, which increased with increased oxidation time and temperature. The surface hardness of the oxide layer at 800 °C was 900 ± 60 HV0.05 owing to the formation of TiO2 and Al2O3 phases. Raw material hardness was 342 ± 20 HV0.05, increasing threefold due to thermal oxidation. In the case of NaCl, weight loss dominated all samples except at 800 °C for 5 h. In the case of NaCl + Na2SO4, weight gain occurred at 600 and 800 °C for 5 h. Weight loss occurred for the raw samples and those processed at 800 °C for 20 and 50 h, where the oxide layer flaked off. Surface hardness increased upon hot corrosion testing because of the formation of brittle phases, such as TiO2 and Na4Ti5O12. Samples that oxidized at 800 °C for 5 h had the highest hardness and corrosion resistance.

Effect of Y Content on Precipitation Behavior, Oxidation and Mechanical Properties of As-Cast High-Temperature Titanium Alloys

To improve the heat resistance of titanium alloys, the effects of Y content on the precipitation behavior, oxidation resistance and high-temperature mechanical properties of as-cast Ti-5Al-2.75Sn-3Zr-1.5Mo-0.45Si-1W-2Nb-xY (x = 0.1, 0.2, 0.4) alloys were systematically investigated. The microstructures, phase evolution and oxidation scales were characterized by XRD, Laser Raman, XPS, SEM and TEM. The properties were studied by cyclic oxidation as well as room- and high-temperature tensile testing. The results show that the microstructures of the alloys are of the widmanstätten structure with typical basket weave features, and the prior β grain size and α lamellar spacing are refined with the increase of Y content. The precipitates in the alloys mainly include Y2O3 and (TiZr)6Si3 silicide phases. The Y2O3 phase has specific orientation relationships with the α-Ti phase: (002)Y2O3 // (1¯1¯20)α-Ti, [110]Y2O3 // [4¯401]α-Ti. (TiZr)6Si3 has an orientation relationship with the β-Ti phase: (022¯1¯)(TiZr)6Si3 // (011)β-Ti, [1¯21¯6](TiZr)6Si3 // [044¯]β-Ti. The 0.1 wt.% Y composition alloy has the best high-temperature oxidation resistance at different temperatures. The oxidation behaviors of the alloys follow the linear-parabolic law, and the oxidation products of the alloys are composed of rutile-TiO2, anatase-TiO2, Y2O3 and Al2O3. The room-temperature and 700 °C UTS of the alloys decreases first and then increases with the increase of Y content; the 0.1 wt.% Y composition alloy has the best room-temperature mechanical properties with a UTS of 1012 MPa and elongation of 1.0%. The 700 °C UTS and elongation of the alloy with 0.1 wt.% Y is 694 MPa and 9.8%, showing an optimal comprehensive performance. The UTS and elongation of the alloys at 750 °C increase first and then decrease with the increase of Y content. The optimal UTS and elongation of the alloy is 556 MPa and 10.1% obtained in 0.2 wt.% Y composition alloy. The cleavage and dimples fractures are the primary fracture mode for the room- and high-temperature tensile fracture, respectively.

Peculiarities of Oxidation of Metals and Alloys by Hydrogen Peroxide in the Presence of Stimulating Additive of Iodine

Peculiarities of Oxidation of Metals and Alloys by Hydrogen Peroxide in the Presence of Stimulating Additive of Iodine

Investigation on the surface reactions of Mg–Al alloy/Teflon/Viton in O2

ABSTRACT A comprehensive study on the surface morphologies and element distributions of Mg–Al alloy particles and Mg–Al alloy/Teflon/Viton composite (MATV) during oxidation was conducted via scanning electronic microscopy and energy-dispersive X-ray spectroscopy. The formations of the reaction products of MATV were further analyzed via X-ray diffraction. By the temperature of 600°C, a fluorination reaction between Teflon and the alloy underwent on the alloy surface, involving the reaction of the αMg prime phase at lower temperature. A MgF2–AlFx shell surrounding the alloy particle was also generated simultaneously. This shell could elevate the oxidation temperature from the melting point of the alloy to 600~859°C. Furthermore, this shell could also severely decrease the oxidation rate of the exceeded alloy with O2. As the slower oxidation of the homogeneous liquid alloy began at higher temperature, a different mechanistic reaction from that of the pure alloy underwent. MgO particles rather than MgO ridges on the pure alloy surface were generated.

Kinetics and Combustion Behavior of Atomized Zn-Mg Alloy Powder.

Using pyrolants instead of warhead charges can release red light and thick smoke for target practice to highlight the safety of the impact point and dud disposal. In order to find the ideal material, the combustion and kinetic properties of two Zn-Mg alloys at critical proportions were investigated. Thermogravimetry/differential scanning calorimetry (TG/DSC) experiments in pure oxygen were conducted with atomized Zn-Mg alloy powder in the ratio of 7:3 and the ratio of 8:2 with three particle diameters under different heating rates. The kinetic parameters of the six materials were obtained by ASTM E698 and Ozawa-Flynn-Wall (OFW) methods, indicating that the activation energy (Eα) of the 7:3 Zn-Mg alloy powder was lower than that of the 8:2 Zn-Mg alloy powder when the particle size distributions are similar. By the method of nonlinear multivariate regression, the oxidation reaction of Zn-Mg alloy powder was divided into two steps. The proportion of mass gain of the first-step reaction of 7:3 Zn-Mg alloy powder was 0.462-0.518, and the proportion of mass gain of the first-step reaction of 8:2 Zn-Mg alloy powder was 0.138-0.228. Reaction mechanism functions of the two-step reaction of Zn-Mg alloy oxidation were derived as f(α) = (1 - α)n(1 + kcat·α). The results of combustion experiments showed that the pyrolants composed of 7:3 alloy can burn stably to produce satisfactory smoke and light signals, while the pyrolants composed of 8:2 alloy cannot achieve this. The 7:3 Zn-Mg alloy powder is an ideal ingredient for pyrotechnic compositions.

An ab-initio study of induced half metallic ferromagnetism in Hf–Nb alloy oxides

An ab-initio study of induced half metallic ferromagnetism in Hf–Nb alloy oxides

The effect of elastic and plastic strain on surface and intergranular oxidation of alloy 600 in simulated PWR primary water

The effects of deformation and stress on the surface and grain boundary oxidation of Alloy 600, exposed to primary water of Pressurized Water Reactors (PWRs), were investigated by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Scanning Electron Microscopy (SEM). It was found that tensile straining prior to oxidation does not modify the surface oxide thickness while the intergranular oxide depth increases when the strain reaches a critical value of 15%. The oxide growth rates at surface and grain boundaries are enhanced under stress. The effect of stress is more significant when the specimen is under elastic strain than plastically deformed.

Ion irradiation of the metal matrix and its effects on the oxidation of the M5Framatome alloy

The good corrosion resistance of the M5Framatome cladding used in pressurised water reactors (PWR) may be due to the irradiation induced modifications of this alloy. Several ion irradiation tests were performed on the M5Framatome alloy to reproduce the in-core metallurgical changes, followed by corrosion tests on the irradiated samples. Proton irradiation experiments at 350 °C produced long, nanometric niobium-rich precipitates. After irradiation, a significant decrease in the oxidation rate could be observed, highlighting the beneficial effect of irradiation on the corrosion behaviour. In addition, the amorphisation of Zr(Nb, Fe)2 intermetallic precipitates did not change the oxidation rate of the M5Framatome alloy.

Analysis of Microstructure and Mechanical Properties of AZ31B Thick Plate Magnesium Alloy Stir Friction Welded Joints

Welding of 10 mm thick AZ31B magnesium alloy by stir friction welding technique. The effects of process parameters on the microstructure, tensile strength and impact resistance of the joints were analyzed. The results showed that the joints were formed with good quality and no obvious defects, and the joints were fine-grained and accompanied by grain dislocations. The grain dislocation in the hot machine influence zone is more obvious there is a dense grain dislocation zone, and the distribution is not uniform. When the spindle speed is 800 and 1000 rpm, respectively, the best impact resistance of the welded joint impact work is 8.02 J, which is about 94.2% of the impact resistance of AZ31B magnesium alloy base material. When the spindle speed is 1000r/min and the welding speed is 150 mm/min, the tensile strength of the welded joint is the largest, reaching 85.8% of the base material and the post-break elongation is 1.9 times that of the base material. Thick plate magnesium alloy plate welded joints overall performance is not uniform, welded plate bottom mechanical properties of the worst, weld core area doped magnesium alloy oxide, joint tensile fracture crack source from the bottom of the plate to the weld surface expansion.

Insights into oxidation and nitridation of alumina-forming FeCrAl alloy after supercritical water exposure: Effect of pre-corrosion on high-temperature damage behavior

This work investigated the corrosion characteristics of FeCrAl alloy in supercritical water (SCW), and focused on the effect of SCW pre-corrosion on the alloy oxidation and nitridation at 900 °C. FeCrAl alloy formed outer Fe-rich oxides (mainly Fe2O3) and inner Fe-Cr-Al oxides during SCW exposure. SCW pre-corrosion made FeCrAl alloy exhibit different morphologies and phase compositions in the same medium. SCW pre-corrosion promoted the deposition of Ni and Mo elements from the autoclave, filling the gaps in flaky oxides by forming Ni- and/or Mo-rich products in air and N2. Moreover, SCW pre-corrosion avoided the appearance of accelerated nitridation zones in N2. However, pre-corrosion caused the preferential diffusion of N2 and air. Outward-diffused Cr ions during SCW exposure reacted with O impurities in N2 to form Cr2O3 that easily dissociated N2, leading to the development of nitridation towards the alloy interior.

Early-stage surface oxidation of the equiatomic CoCrFeMnNi high entropy alloy studied in situ by XPS

The mechanisms of initial oxide growth on the equiatomic CoCrFeMnNi high entropy alloy were studied in situ by X-ray photoelectron spectroscopy on clean, oxide-free surfaces exposed stepwise to low-pressure gaseous oxygen. Cr(III), Mn(III), Fe(III), Co(II) but no Ni(II) oxides were formed at 100 °C, and Mn(II) at 200 °C. Data quantification revealed a transition mechanism from selective initial oxidation to 3D kinetically-controlled growth, leading to stratification of the oxide film. Formation of the Co-rich outer layer above the Cr-rich inner layer first formed implies predominant cationic outward oxide growth supported by the overall stoichiometry of the film.

High-performance catalytic electrode for glucose sensor fabricated by one-step selective oxidation of brass compositions

In this study, three-dimensional nanostructured electrodes were synthesized by one-step electrochemical anodizing of the brass. Composites based on different oxides/hydroxides including ZnO, Cu2O, Cu(OH)2, and CuO are selectively prepared by potential modulation for the first time. With the increase of potential, the nano-oxide transforms from granular morphology into uniformly distributed nanosheet clusters, and the size of the nano-sheet decreases gradually with the increase of potential, finally, the double-layer nanosheet structure is formed. Attributed to the finely regulated composition and nanostructure, high-performance non-enzymatic glucose sensor electrodes are developed, which can exhibit prominent sensitivity for glucose catalytic up to 2817 μA·mM−1·cm−2 with a response time within 3 s and outstanding selectivity. This pioneering work not only offers a promising strategy for the rational construction of high-performance glucose catalytic nanostructured electrodes, but also provides a fresh pathway for the selective oxidation of alloys to form functional materials that meet practical needs.