Parabolic Oxidation Research Articles

Study on the High-Temperature Oxidation of AlCrFeCoNi-Based High-Entropy Alloys with Trace Si Additions

This research investigates the isothermal oxidation behavior of AlCrFeCoNiSix (x = 0, 0.04, 0.08, 0.12at.%) at 900°C for 96hours from multiple aspects, including the oxidation surface, the oxide layer microstructure, and the oxidation mechanisms. The oxidation kinetics curves of the alloys follow the parabolic oxidation law. After 96hours of oxidation at 900°C, the oxide films of the AlCrFeCoNi and AlCrFeCoNiSi0.04 alloys are primarily composed of Al2O3. In contrast, the oxide films of the Si8 and AlCrFeCoNiSi0.12 alloys consist of an outer layer of Cr2O3/spinel oxides and an inner layer of Al2O3.The results show that the third element effect triggered by the addition of Si can promote the generation of an Al2O3 layer, which has a positive effect on the antioxidant of high-entropy alloys.

Characterization of hot‐pressed ZrC–TiC composites

AbstractSynthesis and consolidation of (Zr,Ti)C were investigated in the present work. ZrC–TiC powder mixture was synthesized at 1650°C for 90 min by the carbothermal method. The prepared powder mixture was hot‐pressed at 1800 C for 60 min under a pressure of 40Mpa and then heat‐treated at 2100 C for 60 min. There were ZrC‐rich and TiC‐rich phases together with zirconium oxide phases in powder mixture and hot‐pressed samples, while there were no oxide phases in the heat‐treated sample and only ZrC‐rich and TiC‐rich phases were present in the sample. The FESEM image of the fracture surface of the samples shows that the porosity of the samples decreases with increasing temperature. Relative density, microhardness, and flexural strength increased from 93.8% to 98.6%, from 15.26 to 21.41 GPa, and from 185.02 to 220.69 MPa, respectively, with increasing temperatures from 1800 C to 2100 C. In contrast to these properties, the fracture toughness of the samples was reduced from 3.71 to 3.47 MPa·m1/2. The investigation of oxidation behavior also showed that oxidation is influenced by oxygen diffusion and exhibits nonlinear behavior as a function of time. With increasing oxidation temperature of hot‐pressed and heat‐treated samples from 600 to 1000°C, parabolic oxidation rate constants (kp) increased from .267 to 11.793 and from .367 to 10.993, respectively.

High Temperature Oxidation Behavior of ODS Ferritic Stainless Steel Fe-16Cr-4Al-1Ni-0.4Y<sub>2</sub>O<sub>3</sub>

This study investigates the isothermic oxidation behavior of the new ODS alloy Fe-16Cr-4Al-1Ni-0.4Y2O3 (% by weight) at 700, 800 and 900 °C, with exposure times of 5, 20, 50, and 100 h at each temperature. The purpose is to obtain new data on its high-temperature parabolic oxidation constant for assessing oxidation resistance. The methods used include isothermal oxidation testing, XRD, SEM-EDS characterization, and analysis of oxidation kinetics by monitoring changes in oxide thickness using microscopy and SEM-EDS. The oxide products formed on the sample surface are Fe2O3, Fe3O4, AlFe2O4, and (Fe,Cr)2O3. Al and Cr oxides are located under the dominant Fe oxide layer on the surface of the sample. The oxidation test results showed that the most protective sample was obtained at a temperature of 700 °C for 100 h with an oxide thickness of 263.99 μm. The kinetics analysis correlates strongly with the parabolic equation (R2 ≈ 1). The oxidation rate constants at temperatures of 700, 800, and 900 °C were 681.76, 2957.5, and 12300 μm2 h−1, respectively. The activation energy required by the oxidation reaction in this alloy is 136.5 kJ mol−1. This research enhances understanding and potential applications of the Fe-16Cr-4Al-1Ni-0.4Y2O3 alloy in high-temperature environments.

Cost-effective methods of fabricating thin rare-earth element layers on SOC interconnects based on low-chromium ferritic stainless steel and exposed to air, humidified air or humidified hydrogen atmospheres

Most oxidation studies involving interconnects are conducted in air under isothermal conditions, but during real-life solid oxide cell (SOC) operation, cells are also exposed a mixture of hydrogen and water vapor. For this study, an Fe–16Cr low-chromium ferritic stainless steel was coated with different reactive element oxides – Gd2O3, CeO2, Ce0.9Y0.1O2 – using an array of methods: dip coating, electrodeposition and spray pyrolysis. The samples underwent oxidation experiments carried out over 100 h in three different atmospheres at 800 °C: air, an air/H2O mixture, and an Ar/H2/H2O mixture. The influence of different atmospheres on the corrosion of the Fe–16Cr steel was determined via oxidation kinetics studies; the corrosion product was evaluated using X-ray diffraction, scanning electron microscopy and area-specific resistance (ASR) measurements. All coated samples exhibited lower parabolic oxidation rate constants than bare steel and most also had lower ASR. The applied modifications were found to be sufficiently effective to allow the investigated low-chromium steel to be considered for application as an interconnect material for SOCs.

Stepwise Multi-Temperature Thermogravimetric Analysis (SMT-TGA) for Rapid Alloy Development

A stepwise multi-temperature thermogravimetric analysis (SMT-TGA) method is a rapid and time- and material-efficient measurement procedure for oxidation kinetics over a wide range of temperatures. It is suitable for alloy design and material selection procedures. It involves subjecting a sample to a series of steps at increasing temperatures, followed by steps at decreasing temperatures to identify possible effects on the evolution of oxide layer microstructures on oxidation kinetics. This method has been tested for a wide range of metallic alloys in the present work, allowing for the mapping of possible ranges of parabolic oxidation kinetics of industrial alloys between 600 and 1300°C. Two examples of effects of thermal history have also been described in this publication.

In-situ ETEM study of plasma-facing tungsten nanofuzz oxidation at atmospheric pressure: Microstructure evolution and substrate-free oxidation kinetics

To enable sustainable carbon-free fusion energy, managing reactor structural material degradation during normal operation as well as accident scenarios is vital. Tungsten (W) plasma-facing materials (PFMs) are susceptible to aggressive high-temperature oxidation during air-ingress fusion reactor accidents, yet there's a lack of oxidation kinetic data for irradiated tungsten. Here, we utilize atmospheric environmental transmission electron microscopy (ETEM) to present the first kinetic data for substrate-free W nanofuzz oxidation at 400 °C and 500 °C in 1 bar dry air. Comparison with pristine bulk W during the early parabolic stage suggests an irradiation-decelerated oxidation for W nanofuzz. Our time-resolved in-situ characterization reveals a durable amorphous surface oxide, likely promoted by high-flux He+ irradiation-induced surface defects, serving as an effective passivating layer that impedes nanofuzz oxidation onset. This surface oxide layer also interfaces well with newly formed orthorhombic WO3, facilitated by stress relief through He bubble shrinkage, providing lasting passivating protection throughout the nanofuzz parabolic oxidation. This new finding challenges conventional notions of irradiation's negative impact on metal oxidation, and calls for advanced characterization to enhance our understanding of fusion energy materials degradation, informed by further accident modeling.

Oxidation and wear behaviors of MoNbTaW high entropy alloy fabricated via laser energy deposition at elevated temperature

The microstructure, mechanical properties at room temperature, oxidation, and wear behaviors of the MoNbTaW refractory high-entropy alloy (RHEA) at elevated temperatures are investigated. The as-deposited MoNbTaW RHEA maintains a single BCC structure and a dendritic morphology. Furthermore, it demonstrates a high yield stress of 1478 MPa and an ultimate yield stress of 1787 MPa at room temperature. The oxidation tests reveal that the oxidation rate constant initially decreases from 0.83 mg2 cm−4 h−1 to 0.78 mg2 cm−4 h−1, then increases to 12.43 mg2 cm−4 h−1 as the temperature rises from 500 °C to 800 °C. Additionally, a linear oxidation kinetic is observed at 500 and 600 °C, while at 800 °C, the parabolic oxidation kinetics is observed. The transition is linked to the development of a multilayer oxide layer structure and the formation of a thicker oxide scale. The results of wear tests at high-temperature show that the wear depth at 600 °C is about 24.886 μm, which is 3.9 times as much as 500 °C (6.437 μm). This indicates that the wear resistance is reduced at 600 °C. In addition, with the increase in temperature, the wear mechanism changes from adhesive wear to abrasive wear.

Water accelerates parabolic oxidation of Pu-Ga alloy: from mechanism to model

The moisture accelerated oxidation can endanger the safety storage of plutonium, but experiments haven’t provided a complete mechanism explanation, let alone a prediction model. Based on first principles calculations, this work reveals the acceleration mechanism of water on Pu-Ga alloy oxidation in moist air and interprets available experimental findings. Specifically, the OH adsorption after H2O dissociation can promote the O-vacancy formation in PuO2 by the polaron interaction mechanism, and then facilitate the vacancy diffusion of the actual corrosion medium O after O2 dissociation. Therefore, the diffusion kinetics of O in Pu-oxide is decisive, which is correlated to the relative humidity (RH) and temperature (T). Based on the micro mechanisms and the available experiments, we propose a method to modify the oxidation kinetic model by taking into account the coupling effects of RH and T, this model provides a new way to evaluate and predicts the acceleration ratio of RH and T on the oxidation kinetics of Pu-Ga alloy. This work comprehensively reveals the acceleration mechanism of moisture and then proposes the oxidation kinetic model, which is significant to the storage and protective of nuclear materials.

High‐temperature oxidation of Cu–Al–Ni–Mn shape‐memory alloy

AbstractThe isothermal oxidation behavior of the Cu‐11.35Al‐3.2Ni‐3.5Mn (wt.%) shape‐memory alloy (SMA) in the temperature range of 500–900°C in oxygen was studied using the thermogravimetric (TG) method. TG curve showed that the alloy has parabolic isothermal oxidation characteristics. The effect of oxidation on the surface morphology and chemical composition of the Cu–Al–Ni–Mn alloy was determined by scanning electron microscopy, energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy (XPS) analyses. The oxidation rate of SMA increases up to 700°C, remains stable at 800°C, and increases again up to 900°C. The XPS analysis identified that the corrosion products mainly contained MnO2, MnO/Mn2O3, and Al2O3.

Unveiling the diffusion pathways under high-temperature oxidation of Cr2AlC MAX phase via nanoscale analysis

The MAX phase chromium aluminium carbide (Cr2AlC) is a potential candidate for high-temperature structural and energy applications due to the unique combination of properties, including excellent oxidation and corrosion resistance in harsh environmental conditions. In this work, the oxidation behaviour of bulk Cr2AlC was studied at temperatures of 1000 °C and 1200 °C in humid synthetic air, mimicking a realistic application environment. An α-Al2O3 scale forms at both temperatures, consisting of both inward and outward-growing layers, with a continuous Cr7C3 layer beneath the oxide. A special focus was put on employing atom probe tomography (APT) to analyse the oxide and carbide layers at the nanoscale. Decomposition of Cr2AlC to Cr7C3 is the main source (>70%) of aluminium needed for the oxide scale formation, while Al depletion in the underlying MAX phase remains marginal (<1 at%), exhibiting a pattern different from the common high-temperature oxidation of alloys. Al diffusion to the oxide scale proceeds predominantly through grain boundaries (GBs) in Cr2AlC and through the bulk in Cr7C3. Ionic diffusion through GBs of the large-grained inner alumina layer seems to be the rate-limiting step for the oxide scale growth, resulting in the apparent parabolic oxidation kinetics. No segregation of Cr, C or any impurities, which could affect ionic transport, was found at these alumina GBs by APT, rendering the results of this study as characteristic of a pure Cr2AlC oxidation.

Lead-bismuth eutectic corrosion behavior of NbMoVCr refractory multi-principal element alloys coating synthesized by magnetron sputtering

Nanocrystalline NbMoVCr refractory multi-principal element alloys coatings are fabricated by magnetron sputtering technology to improve lead-bismuth eutectic (LBE) corrosion resistance of structural materials, and their corrosion behavior in oxygen-saturated liquid LBE at 600 and 650 °C has been investigated. The coatings exhibit good phase structural stability even at 650 °C exposure. Moreover, the coatings show promising LBE corrosion resistance with parabolic oxidation rate constant 3–5 orders of magnitude lower than other candidate steels (such as 316 L, HT9, T91, SIMP, CLAM, etc.) which is due to the formation of protective (CrV)2O3 solid solution layer. The oxidation process of the coating is mainly dominated by kinetic factors, including diffusion driving force (related to LBE solubility) and diffusion energy barrier (related to atomic radius). By the way, at the grain boundaries with much lower oxygen potential, thermodynamic factors dominate the oxidation process, and V with the highest oxygen activity shows evidence of selective oxidation.

Effect of intermetallic compounds on the high-temperature oxidation resistance of Al0.25CoCrFeNiCuAux (x = 0, 0.1, 0.3) high-entropy alloys

In this work, the effect of gold alloying on the microstructure, phase composition, and high-temperature oxidation resistance of Al0.25CoCrFeNiCu high-entropy alloy (HEA) was studied. It is shown that gold is partly incorporated in the dendritic face-centered cubic (fcc) phase, and it is mainly precipitated as intermetallic compounds (ICs) in the interdendritic space. Al2Au and AuCu3 ICs could be precipitated depending on the concentration of gold. The formation of Al2Au ICs increased the parabolic oxidation rate constant (kp) from 378.5 × 10–13 (g2/cm4s) for Al0.25CoCrFeNiCu to 1079.5 × 10–13 (g2/cm4s) for Al0.25CoCrFeNiCuAu0.1 HEA, while the precipitation of AuCu3 in Al0.25CoCrFeNiCuAu0.3 HEA reduced this index to kp = 94.9 × 10–13 (g2/cm4s). Microstructural analysis of the oxidized samples revealed that binding of aluminum into Al2Au IC decreases the amount of available aluminum in the solid solution phase to form a protective Al2O3 oxide layer on the surface of Al0.25CoCrFeNiCuAu0.1 alloy during high-temperature oxidation. On the contrary, the binding of copper with gold into AuCu3 IC effectively prevents Cu from oxidation and provides routes for the formation of a dense layer of Al2O3 oxide with superior protective properties.

Revealing the effect of Gd alloying on oxidation resistance and oxide film protection performance of AZ80 alloy

The high-temperature oxidation behaviors and oxide film characteristics as well as corrosion protection of AZ80 and AZ80–0.75Gd (wt%) alloys were investigated to research the effect of Gd addition on oxidation resistance and oxide film corrosion protection performance of AZ80 alloy. The results showed that with 0.75 wt% Gd alloying, Gd2O3 appeared in oxide film, which promoted densification of oxide film and translation of the superlinear rate law oxidation kinetics to approximate parabolic rate law oxidation kinetics of alloy. And after erosion of oxide film containing Gd2O3, the corrosion products were extensively nodulated, resulting in corrosion passivation and showing protection effect.

Exploring the oxidation behaviors of the Ti[sbnd]V[sbnd]Cr[sbnd]Mo high-entropy MAX at 800 °C for its self-lubricity

Given the unique nanolaminate structure, the MAX phase ceramics which are composed of alternatively stacked two-dimensional (2D) metal (M) carbides (X) and main group (A) atomic layers have shown promising properties at elevated temperatures. Recently, an excellent self-lubricating performance of a high-entropy (HE) (TiVCrMo)3AlC2 MAX is demonstrated at 800 °C in the air. However, the formation mechanism of a self-lubricative tribofilm is still waiting for clarified. In this work, the HE (TiVCrMo)3AlC2 MAX is synthesized and its oxidation behaviors are systematically evaluated at 800 °C in the air. A two-stage parabolic oxidation behavior is detected, which can be mainly ascribed to the volatilization of MoO3 species coupled with the thickening of the compound oxide scale. Meanwhile, the HE composition results in chemically complex phases including Rutile and vacancy-ordered TiO species in the oxide scale, which contribute to a higher ion diffusion rate for mass transportation. Consequently, the continued volatilization of MoO3 is beneficial for the enhanced lubricity and anti-wear performance of the (TiVCrMo)3AlC2 MAX at 800 °C.

High-temperature oxidation behavior of laser additively manufactured AlCrCoNiSi-based high-entropy alloys at 1100 ℃

High-temperature oxidation behavior of two laser additively manufactured AlCrCoNiSi-based high-entropy alloys (Al10 and Al15) are systematically studied in this work. These two alloys exhibit similar oxidation behaviors involving initial linear kinetics oxidation and subsequent parabolic kinetics oxidation at 1100 ℃. However, Al10 alloy has a superior oxidation resistance than Al15 alloy according to the oxidation rate constant. α-Al2O3 is the predominant phase of the oxide scales grown on both alloys. Cross-sectional views of the scales show that the scales consist of surface equiaxed grains and underlying columnar grains. For all oxidized alloys, a newly-formed fcc layer forms in the subsurface Al-depletion zone due to the preferential oxidation of aluminum. Al10 alloy exhibits a much thicker newly-formed fcc layer than Al15 alloy after the same oxidation time. This work ascribes the superior oxidation resistance of Al10 alloy to its thick newly-formed fcc layer, which suppresses the outward Al diffusion from the substrate to scale-metal interface by increasing the diffusion distance.

Unraveling the oxidation behavior and mechanism of (TiZrTaNbCr)C high-entropy ceramic by introducing Cr3C2

High-entropy carbide ceramic materials exhibited excellent thermal and mechanical properties, making them highly sought after in high-temperature applications. However, the oxidation resistance of high-entropy carbide ceramic needed to be further improved. This work unraveled the oxidation behavior and mechanism of high-entropy carbide ceramic by introducing the Cr3C2. The results indicated that the oxidation rate of (TiZrTaNbCr)C initially decreased with temperature up to 900 °C, followed by an increased with further temperature rise up to 1100 °C. At 800 and 900 °C, the parabolic oxidation rate constants were 0.70 and 0.17 mg2cm−4min−1, respectively. And the minimum thickness of oxidized layer was 60 µm at 900 °C for 120 min. This unusual phenomenon suggested the formation of different oxidation products. Specifically, the CrNbO4 and Nb2Zr6O17 oxide layer were formed at 900 °C, leading to an increased resistance to oxygen diffusion. Subsequently, loose oxidation products of Nb2O5 were formed after 1000 °C, hindering the oxidation resistance. In the current study on oxidation resistance of high entropy carbides, this work showed a competitive performance. Overall, this study illustrated the oxidation mechanism and behavior of (TiZrTaNbCr)C and proposed a new avenue for the design of high-entropy ceramic components.

High-temperature oxidation behaviour of a Co-based superalloy fabricated through laser powder bed fusion

This study investigated the oxidation behaviour of a Co-based superalloy fabricated through laser powder bed fusion at 900 ℃. In terms of oxidation products, the results revealed the generation of basic oxides, such as CoO, Al2O3 and TiO2, and Co-containing spinels, such as CoAl2O4 and Co2TiO4. Heat treatment improved oxidation resistance by reducing the parabolic oxidation rate constant from 0.17234 to 0.10032 mg2 cm−4 h−1. γ′ precipitates, twin boundaries and less spallation in the heat-treated sample contributed to this improvement, leading to a superior oxidation resistance in this study than in previously reported Co-Al-W-based alloys.

Delayed parabolic oxidation via transient thermal exposures on a polycrystalline nickel-based superalloy

Multiple oxides were observed during the transient oxidation stage of the polycrystalline Ni-based superalloy, RR1000, before a protective Cr2O3 scale formed. Thermogravimetric analysis, synchrotron grazing incidence X-ray diffraction, and electron microscopy were performed on samples subjected to isothermal exposures at 800 °C for up to 100 h. Transient effects governed the early stages up to 40 h. NiO, spinels (NiCr2O4, (Ni,Co)(Cr,Co)2O4), Cr2O3/(Cr0.88Ti0.12)2O3, NiTiO3, and CrTaO4 formed during the initial stage with pseudo-linear kinetics. At the onset of parabolic kinetics, extensive Cr2O3 and TiO2 growth dominated scale formation with the former emerging as the major passivating oxide.

Neutral Phenolic Contaminants Are Not Necessarily More Resistant to Permanganate Oxidation Than Their Dissociated Counterparts: Importance of Proton-Coupled Electron Transfer.

Despite decades of research on phenols oxidation by permanganate, there are still considerable uncertainties regarding the mechanisms accounting for the unexpected parabolic pH-dependent oxidation rate. Herein, the pH effect on phenols oxidation was reinvestigated experimentally and theoretically by highlighting the previously unappreciated proton transfer. The results revealed that the oxidation of protonated phenols occurred via proton-coupled electron transfer (PCET) pathways, which can switch from ETPT (electron transfer followed by proton transfer) to CEPT (concerted electron-proton transfer) or PTET (proton transfer followed by electron transfer) with an increase in pH. A PCET-based model was thus established, and it could fit the kinetic data of phenols oxidation by permanganate well. In contrast with what was previously thought, both the simulating results and the density functional theory calculation indicated the rate of CEPT reaction of protonated phenols with OH- as the proton acceptor was much higher than that of deprotonated phenols, which could account for the pH-rate profiles for phenols oxidation. Analysis of the quantitative structure-activity relationships among the modeled rate constants, Hammett constants, and pKa values of phenols further supports the idea that the oxidation of protonated phenols is dominated by PCET. This study improves our understanding of permanganate oxidation and suggests a new pattern of reactivity that may be applicable to other systems.

Oxidation behavior of Si-C-O-(Ti) fibers from 450° to 1140°C: Comparing the kinetic of oxide scale growth to the slow crack growth

The oxidation behavior of Tyranno® Grade-S SiC-tows was investigated under ambient air in the 450–1140 °C range. Below 650 °C, a linear oxidation rate was identified for oxide scale thicknesses up to 1.2 µm, attributed to the hydroxyl (Si-OH) groups degrading the silica structure as shown by 1H and 1H–29Si CP/MAS NMR. Above this temperature, the classical parabolic oxidation rate (diffusion controlled) was identified with a dehydroxylated silica scale. These results bring new insights to interpret the slow crack growth (SCG) transition observed at 650 °C. Above 650 °C the activation energies (Ea) for oxidation and SCG are close to 50 kJ mol−1 indicating the diffusion might be the rate limiting factor; whereas for lower temperatures EaSCG < Eaoxidation as a consequence of the stress-enhanced chemical reactivity. The oxide thicknesses at failure time (predicted with power or exponential laws) were assessed and highlight some incoherencies in the lifetime projection to lower stresses.