Oxidation Of Alloys Research Articles

Influence of Plasma Electrolytic Oxidation of Cast Al-Si Alloys on Their Phase Composition and Abrasive Wear Resistance

The microhardness and abrasive wear resistance of cast Al-Si alloys after plasma-electrolytic oxidation (PEO) in a weakly alkaline basic electrolyte (3 g/L KOH + 2 g/L Na2SiO3), as well as with the addition of H2O2, were determined. X-ray analysis showed that the PEO layer comprises two oxide phases, namely α-Al2O3 and γ-Al2O3, as well as sillimanite -Al2O3 · SiO2 and a small percentage of mullite -3 Al2O3 · 2SiO2. Silicon is present in the structure of the oxide layer, and its percentage is greater than that of the alloys in their initial state. It has been shown that the characteristics of PEO layers on AK9 and AK12 silumins synthesized in an electrolyte of basic composition increase (microhardness up to 900–1000 HV and abrasive wear resistance by 14–57 times). The formation of PEO layers in the base electrolyte with the addition of 3 g/L of hydrogen peroxide intensifies the synthesis process and promotes the formation of high-temperature oxide phases (in particular, corundum). The abrasive wear resistance of both silumins with PEO layers synthesized in such an electrolyte increases by 30–70%.

CeO2 promotes electrocatalytic formic acid oxidation of Pd-based alloys

Engineering metal/oxide interface and controlling composition are the important strategies that aim towards obtaining efficient Pd-based electrocatalysts (ECs). Rationally designed ECs for dehydrogenation of formic acid play a dynamic role in the proper utilization of its chemical energy. Herein, we report Pd3M alloy nanoparticles anchored on CCeO2 (Pd3M/CCeO2, M = Cu, Ni, Co) which shows significant performance towards formic acid oxidation (FAO). Interestingly, Pd3M/CCeO2 (M = Cu, Ni, Co) ECs displayed the best FAO activity via the “dehydrogenation” pathway. The remarkable performance can be mainly attributed to the proper electronic and synergistic effects between Pd and the alloyed metal, which leads to Pd lattice contraction and downshift of d-band center. It was also observed that the FAO activity of Pd3Cu/CCeO2 is superior to that of Pd3Co/CCeO2 and Pd3Ni/CCeO2. The oxygen vacancies in CeO2 and strong Pd/CeO2 interactions established by computational and experimental studies contribute towards the overall electrocatalytic behaviour.

Multi-method characterization of anodic oxidation of a titanium alloy in fluoride-containing electrolytes

Multi-method characterization of anodic oxidation of a titanium alloy in fluoride-containing electrolytes

Inconel®625 oxidation in CO2: Kinetics and reaction mechanism

Inconel®625 oxidizes in CO2 from about 750 °C. The reaction, studied at the beginning, does not depend on the CO2 pressure. Between 900 and 1000 °C, and for weight increases < 0.5 mg/ cm², the oxidation is parabolic forming chromia layers. The components nickel and molybdenum do not oxidize. The apparent activation energy is 310 ± 18 kJ / mol. Unlike what is usually admitted for the oxidation of chromia-forming alloys, the chromia layer does not protect the alloy, the limiting step of the oxidation being the outwards diffusion of chromium inside the alloy, not inside the oxide layer.

Ultra-rapid and long-lasting activation of peracetic acid by Cu-Co spinel oxides for eliminating organic contamination: Role of radical and non-radical catalytic oxidation

Peracetic acid (PAA)-based advanced oxidation processes (AOPs) have attracted considerable attention in organic wastewater purification for yielding reactive oxidative species (ROS) with high performance and long lifetime. However, searching for economical and stable activators is a huge obstacle. In this work, we used a facile second transition metal embedding approach to prepare bimetallic spinel oxides (CuCo2O4) through embedding Cu to Co3O4, which was used as the activator for the rapid and durable activation of PAA to remove model organic pollutant bisphenol A (BPA). Under identical conditions, the rate constant of the constructed CuCo2O4/PAA system (0.0412 min−1) was 21.7 and 3.3 times that of CuO/PAA (0.0019 min−1) and Co3O4/PAA (0.0125 min−1) system alone, respectively. The CuCo2O4/PAA system had better resistance to co-existed ions and natural organic compounds. Meanwhile, the as-prepared materials maintained excellent stability during four-cycle tests and gradient experiments, confirming their perfect application potential. Combining the capture experiments, chemical probe, electron paramagnetic resonance, and theoretical calculations, the singlet oxygen (1O2) and organic radicals (R-O•, e.g., CH3C(O)O• and CH3C(O)OO•) were validated to be the dominant ROS. The density functional theory (DFT) calculations indicated that both BPA and PAA were more easily adsorbed onto the CuCo2O4 surface and bimetallic internal cycle opening was more likely to occur, which accelerated the PAA activation and the contaminants decomposition for rapid electron supply. This study provides new ideas for the design of alternative alloy oxides as efficient PAA activators, and further broadens the applicability of non-homogeneous PAA-based AOPs in wastewater decontamination.

Interface engineering of LDH-based material as efficient anti-corrosive system via synergetic performance of host, interlayers, and morphological features of nature-mimic architectures

High-performance hybrid materials with special features are desired to meet the requirements of more complex cutting-edge applications. However, the self-assembly of layered double hydroxides (LDH) with organic frameworks is hampered by a lack of understanding of the formation mechanism and the effects of the self-assembled architecture on anticorrosion activity remain a major challenge. Herein, we put forward how the honeycomb-like network would architecturally upgraded on the pre-existing hierarchical floral structure with Trimesic acid (TMA) compound resulting in a promising layer-by-layer (LBL) material. This nature-inspired network is realized to offer an ideal approach not only endows with excellent properties but also exploits the power of layered coating materials as a bastion in the fields of nanotechnology, without limiting conditions, taking advantage of the synergy beneficial effects of the self-assembled honeycomb-like TMA and the anion-exchange ability of the layered coating material. In this work, a three-dimensional assembly with an architecture closely resembling interconnected micro-petals was successfully deposited on the defective surface obtained via plasma electrolytic oxidation (PEO) of Mg alloy, where TMA compound was used for supramolecular self-assembly. The MgO layer was first formed on AZ31Mg alloy via PEO treatment and the Mg-Al LDH micro-petals were synthesized on the MgO surface in the presence of a chelating agent [diethylenetriaminepentaacetic acid (DTPA)]. In a typical synthesis, TMA compound was used as an appropriate linker for the formation of well-organized multidimensional layered materials taking advantage of the synergy beneficial effects of the self-assembled honeycomb-like TMA and the anion-exchange ability of the Mg-Al LDH coating. The results indicate that Mg alloy coated with the self-assembled TMA@LDH-MgO materials presents excellent anti-corrosion performance as compared to the bare Mg. The use of such system would open a brand-new possibility to correct, in a targeted way, the inevitable defects of the layered coating morphology while retaining its exceptional potential. First-principles calculations, quantitative molecular surface analyses and independent gradient model framework further verify the self-assembly and adsorption behavior of TMA over the Mg-Al LDH layer. The improved performance of the TMA@Mg-Al LDH film is attributed to the synergistic effects of different interactions that occurred around active sites in the hierarchical network.

Effect of pressure on high-temperature oxidation of Ni alloys in supercritical CO2 containing impurities

Direct supercritical CO2 (sCO2) power cycles require structural materials compatible with hot sCO2 containing high levels of water and oxygen impurities. Chromia-forming Ni-based superalloys, which are leading candidates at temperatures > 600 °C, have shown good compatibility in pure sCO2, however potential impurity effects are not well understood. Herein we exposed several commercial Ni-based alloys to 95%CO2-4%H2O-(1−3)%O2 at 750 °C and 0.1 or 20 MPa for 2500 h. Protective chromia scales formed in all cases. Nevertheless, water vapor-assisted oxide volatilization clearly occurred at high pressure. The volatilization rates decreased with time, but still represent a potentially serious compatibility issue in real, high-velocity, sCO2 systems.

Hot compression bonding behavior and constitutive model of spray deposited 2195 Al-Cu-Li alloy

Hot compression bonding (HCB) tests of spray deposited 2195 Al-Cu-Li alloy were carried out under different temperatures and strain rates when the sample chamber was vacuumized to 1.0 × 10−3 Torr. The constitutive models and processing map during HCB process were established, and interfacial microstructure, especially the oxide film evolution and bonding mechanism of this alloy were investigated. The results showed that this alloy possesses both good bondability and stable deformation ability in three deformation parameter regions, with a temperature of 500 °C and strain rates of 0.01–0.05s−1 and 1–10s−1, and temperature of 430–470 °C and strain rate of 0.05–0.55 s−1. The interface of this alloy forms oxide film even under near vacuum environment, and the oxide films are predominantly amorphous Al2O3 and nanocrystalline of γ-Al2O3, and a small amount of Li2CO3, Al(OH)3, MgAl2O4. The strain rate influences bonding mechanism dramatically, when samples are compressed at high strain rate, the interfacial healing was highly dependent on microplastic deformation and mechanical interlock around the interface. While compressed at low strain rate, the interfacial healing was mainly dependent on grain boundary bulging or particle-stimulated nucleation, grain boundary migration and dynamic recrystallization (DRX).

Phase-field modeling of alloy oxidation at high temperatures

Oxide growth is a complex process involving transport of reactive species, heterogeneous reactions, and microstructure evolution. Predicting oxidation kinetics, especially the oxide morphological change has been a longstanding challenge. Here we develop a phase-field model for predicting the oxide growth kinetics of a multicomponent alloy during high temperature oxidation, focusing on internal oxidation (non-protective) and its transition to external oxidation (protective). The predicted kinetics and oxide morphology are analyzed and compared to the classical Wagner's theory and an existing analytical model by Zhao and Gleeson. Some assumptions used in the analytical models and the limitation are discussed. In addition, it is demonstrated that the morphology and distribution of the initial oxide nuclei play an important role in the later stage oxide connectivity and thus the transition to external oxidation.

Study on Electrochemical Properties of Carbon Submicron Fibers Loaded with Cobalt-Ferro Alloy and Compounds

In this work, carbon submicron fiber composites loaded with a cobalt-ferric alloy and cobalt-ferric binary metal compounds were prepared by electrospinning and high temperature annealing using cobalt-ferric acetone and ferric acetone as precursors and polyacrylonitrile as a carbon source. The phase transformation mechanism of the carbon submicron fiber-supported Co-Fe bimetallic compound during high temperature annealing was investigated. The electrochemical properties of the carbon submicron fiber-supported Co-Fe alloy and Co-Fe oxide self-supported electrode materials were investigated. The results show that at 138 °C, the heterogeneous submicron fibers of cobalt acetylacetonate and acetylacetone iron began to decompose and at 200 °C, CoFe2O4 was generated in the fiber. As the annealing temperature increases further, some metal compounds in the carbon fiber are reduced to CoFe2O4 alloy, and two phases of CoFe2O4 and CoFe-Fe-alloy exist in the fiber. After 200 cycles, the specific capacity of CF-P500 is 500 mAh g−1. The specific capacity of the composite carbon submicron fiber electrode material can be significantly improved by the introduction of CoFe2O4. When the binary metal oxides are used as electrode materials for lithium-ion batteries, alloy dealloying and conversion reactions can occur at the same time in the reverse process of lithium intercalation, the two reactions form a synergistic effect, and the cobalt-iron alloy in the material increases the electrical conductivity. Therefore, the carbon submicron fiber loaded with CoFe2O4/CoFe has an excellent electrochemical performance.

The transformation of fretting corrosion mechanism of zirconium alloy tube mating with 304 stainless steel in high temperature high pressure water

Studying the fretting wear mechanism of zirconium alloy in high temperature high pressure water is of great importance for understanding the failure behavior of fuel assembly. In this work, the tangential fretting wear of zirconium alloy tube at different displacement amplitudes (40 µm and 80 µm) and normal forces (6 N and 12 N) was investigated in high temperature high pressure water. The results show that the wear depth and wear volume of zirconium alloy tested at 6 N-80 µm are the highest among all the tests. When the testing condition is 6 N-80 µm, the fretting is located in the gross slip regime. Oxidation and abrasive wear dominate the fretting wear behavior. The increase in normal force and decrease in displacement reduces the relative sliding distance between the contact interfaces, which reduces the ejection of wear debris and changes the wear mechanism. When the test conditions are 6 N-40 µm and 12 N-40 µm, the fretting regime is located in the partial slip regime, and the dominant wear mechanisms are adhesive wear and oxidation. Under the synergistic effect of mechanical wear and high-temperature water corrosion, a dual-layer structure oxide scale is formed on the worn area. The mixed oxide layer with loose and porous structure is formed by the accumulation of granular wear debris, while the dense inner oxide layer is mainly formed by oxidation of the matrix alloy. Fretting wear accelerates material corrosion by wear debris refinement and cracking. The integrity of the oxide layer is negatively correlated with its thickness. As the thickness of the oxide layer increases, more cracks can be observed in the oxide layer.

Kinetics of the Oxidation of Zn55Al Alloy with Molybdenum in the Solid State

Results are presented from studying the kinetics of oxidation of Zn55Al alloy with molybdenum in the solid state. Kinetic parameters of the oxidation of alloys in the 523–623 K range of temperatures are established. It is shown that the behavior of the alloys with a third component differs considerably from the one observed during the oxidation of the binary alloy, with molybdenum additives in amounts of 0.01–0.1 wt % greatly reducing the oxidizability of Zn55Al alloy. Protective films of oxides Al2O3, ZnO, ZnAl2O4, Al2O3·Mo2O3 form during the oxidation of hard alloys.

Kinetics of the Oxidation of Zn55Al Alloy with Molybdenum in the Solid State

Kinetics of the Oxidation of Zn55Al Alloy with Molybdenum in the Solid State

Numerical Model For Short-Time High-Temperature Isothermal Oxidation of Fe–Mn Binaries at High Oxygen Partial Pressure

Since the oxidation reactions in the process of steel production occur in harsh conditions (i.e., high temperatures and gas atmospheres), it is practically impossible to observe in situ the compositional changes in the steel and the formed oxide scale. Hence, a coupled thermodynamic-kinetic numerical model is developed that predicts the formation of oxide phases and the composition profile of the steel alloy’s constituents in a short time due to external oxidation. The model is applied to high-temperature oxidation of Fe–Mn alloys under different conditions. Oxidizing experiments executed with a thermogravimetric analyzer (TGA) on Fe–Mn alloys with different Mn contents (below 10 wt %) are used to determine kinetic parameters that serve as an input for the model. The mass gain data as a function of time show both linear and parabolic regimes. The results of the numerical simulations are presented. The effect of different parameters, such as temperature, Mn content of the alloy, oxygen partial pressure, and oxidizing gas flow rate on the alloy composition and oxide phases formed, is determined. It is shown that increasing the temperature and decreasing the oxygen partial pressure both lead to a thicker depleted area.

The effect of amorphous coating on high temperature oxidation resistance of Ni-based single crystal superalloy

Amorphous Al2O3 coating was prepared on Ni-based single crystal superalloy via atomic layer deposition (ALD) for high temperature oxidation protection. The oxygen inward transport and outward-cation diffusion were hindered by amorphous Al2O3 coating, and the coated alloy showed high oxidation resistance. The low oxygen partial pressure at the alloy/coating interface altered the alloy oxidation behavior, allowing the priority oxidation of protective Al and Cr elements. The oxidation process was controlled by the growth of Cr2O3 and Al2O3. The coating exhibited high spallation resistance. Degradation of the coating, the formation of NiAl2O4 phase in amorphous Al2O3 layer, was observed.

Data-driven predictive modeling of FeCrAl oxidation

FeCrAl alloys are among the most promising candidates for accident-tolerant fuel cladding material in light water nuclear reactors. Despite their high-temperature oxidation resistance in corrosive environments coupled with their hydrothermal corrosion resistance, a key challenge remains in optimizing the composition of the alloy that can be achieved through statistical analysis. However, the current literature on FeCrAl alloy design lack studies for designing alloys based on oxidation resistance. This study addresses that gap by developing a predictive model for the oxidation of FeCrAl alloys based on an experimental dataset, which lays the groundwork for model-based optimization for alloy composition.

Micro- and macro-scale characterization of the microstructure and scratch resistance of the 5083-anodic aluminum oxide film

This paper focuses on the thickness, microstructural, and scratch resistance of the sulfuric oxide layer of 5083-aluminum alloy for different anodizing durations/reaction times (RT = 30, 60, and 90 min). The thickness and the microstructure analyses were carried out using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and ImageJ post-processing software. The scratch resistance was investigated using macro- and micro-scratch tests. Experimental results revealed that the oxide layer was covered by larger-sized microcavities and a thicker oxide layer for 90 min RT. Moreover, the area, which was covered by microcavities percentage, was decreased for 60 min RT and increased for 90 min RT. Besides, using the macro-scratch test, and when increasing RT, no micro-cracks were detected inside the scratch mark. Nerveless, the increasing of the normal load was shown that the oxide layer was more resistant to scratch. Finally, the 5083-aluminum alloy oxide layer had a high-scratch resistance such as a weak penetration depth and a low friction coefficient.

High-Temperature Steam Oxidation of Accident-Tolerant Cr/Mo-Coated Zr Alloy at 1200–1400 °C

The oxidation resistance under LOCA conditions of bilayer Cr/Mo coating deposited on Zr-1Nb zirconium alloy was investigated in this paper. The bilayer Cr (8 μm)/Mo (3 μm) coatings were deposited by magnetron sputtering. Then, oxidation resistance under high-temperature oxidation at 1200–1400 °C in a water steam was studied. The use of a Mo sublayer resulted in limiting Cr-Zr interdiffusion under high-temperature oxidation. It was shown that the Mo barrier sublayer (~3 μm) can provide the protective behavior of the Cr/Mo-coated Zr at 1330 °C in a water steam for at least 720 s. The weight gain of the bilayer Cr/Mo samples was comparable with the monolayer Cr samples after oxidation at 1400 °C. In addition, the analysis of the Cr/Mo-coated Zr alloy oxidation behavior at 1400 °C was carried out.

Chemomechanical finite element analysis for surface oxidation of Aluminum alloy

Chemomechanical finite element analysis for surface oxidation of Aluminum alloy

Циклические закономерности проявления акустической эмиссии при плазменно-электролитическом оксидировании Al–Mg сплава в биполярном режиме

The paper analyzes the features of the acoustic emission (AE) signal generation during plasma-electrolytic oxidation (PEO) of the AMg6 aluminum alloy in a bipolar (anode-cathode) pulsed mode within each cycle of voltage application. The authors studied the range of PEO modes that almost completely covers all standard technological modes for processing aluminum alloys by the current densities (6–18 A/dm2) and current ratio in half-cycles (0.7–1.3), which allowed fixing and studying the AE accompanying the formation of oxide layers for various purposes. For the first time, due to AE registration, a new PEO stage was identified, in which there was no microarc breakdown to the substrate, but which was accompanied by an increase in the layer thickness, and the nature of which has not yet been determined. According to the known features of the oxidation stages, the authors systematized the repetitive forms of AE manifestation in the cycles of exposure and identified their five types and three subtypes. The study shows that the approach used to establish the PEO stages by the “acoustic emission amplitude” parameter has poor accuracy, since it does not take into account the form of signals and the half-period of their registration. Therefore, the authors developed and tested a new approach for analyzing AE frames synchronously with the cycles of change in the forming voltage during PEO, and proposed a new “acoustic-emission median” parameter, which allows identifying the main types and subtypes of signals accompanying the oxidation stages. An experimental study of the proposed AE parameter was carried out to identify these PEO stages, which confirmed the operability, high accuracy and sensitivity of the proposed parameter to the subtypes of AE signals recorded at the cathode stage of “soft sparking”. The latter is of particular interest, since it is a means of studying a given oxidation stage with a resolution equal to the exposure cycle.