Oxide Scale Morphology Research Articles

Water vapor oxidation of SiC layer of tristructural isotropic particles

AbstractTristructural isotropic (TRISO) fuel particles, developed for use in high‐temperature gas‐cooled nuclear reactors, can be subjected to oxidizing environments in off‐normal accident scenarios. In this study, surrogate TRISO fuel particles were oxidized at 1000–1350°C for 4 h in 20 kPa water vapor atmosphere balanced with ultrahigh‐purity helium gas. The oxide scale morphology and thickness were studied via scanning electron microscopy, focused ion beam, and transmission electron microscopy. The oxide thickness increased as the oxidation temperature was increased. Although the oxide scale at 1000°C was completely amorphous, pockets of crystalline oxide were observed on particles oxidized at 1200 and 1300°C. Kinetic analysis was performed to deduce the oxidation mechanism by determining the apparent activation energy using linear regression analysis. The oxidation mechanism was consistent for temperatures from 1000 to 1200°C with an activation energy of 412.4 ± 8.8 kJ/mol. The activation energy then dropped to approximately 201 ± 7.1 kJ/mol for temperatures 1200–1350°C. Therefore, there is a change in oxidation mechanism at ∼1200°C. This change is attributed to the existence of a network of significant bubbles in the oxide layer at higher temperatures, which serve as rapid diffusion pathways for the transport of oxidants from the surface to the SiC/SiO2 interface, instead of relying on the bulk diffusion through the SiO2 layer at lower temperatures where only small bubbles are present along the SiC/SiO2 interface.

Oxidation Behaviour of TiC/TiN Coatings Deposited by Chemical Vapor Deposition (CVD): Mechanisms, Structures, and Properties

This review explores the oxidation behavior of Titanium Carbide (TiC) and Titanium Nitride (TiN) coatings deposited by Chemical Vapor Deposition (CVD), with a focus on their industrial applications as wear-resistant coatings for cutting tools. It examines effect of process parameters—such as temperature, pressure, precursor composition, and substrate preparation—on formation and performance of TiC/TiN coatings. The review evaluates the microstructural characteristics of these coatings, including crystal structure, using X-ray diffraction analysis. Also, estimates the mechanical properties such as hardness, wear resistance, and adhesion strength. Additionally, the review covers the thermal stability of TiC/TiN coatings, emphasizing their ability to maintain structural integrity at high temperatures, which is essential for the performance of cutting tools and other industrial components. A major focus is the oxidation behavior of TiC/TiN coatings, including the impact of coating composition, deposition methods, and environmental conditions. The review details oxidation kinetics and mechanisms, revealing various stages of oxidation at different temperatures. It also examines oxide scale morphology and its effect on coating properties. Finally, this review reveals the importance of alloying elements, like silicon, in improving oxidation resistance. Composite coatings such as TiSiN and TiSiCN are shown to offer better high-temperature stability compared to traditional TiN coatings. The effects of coating thickness and the benefits of multilayer coatings for enhanced oxidation resistance are also discussed.

Comparative study on the oxidation behavior of Si2BC3N/Ta4HfC5 ceramics at 1000 °C and 1500 °C: Microstructural evolution and kinetics consideration

The oxidation kinetics and oxide scale morphology of the Si2BC3N/Ta4HfC5 ceramics sintered by hot-pressing were explored at 1000 °C and 1500 °C in flowing air. Dense Si2BC3N/Ta4HfC5 ceramic sintered at 1900 °C with fine grain sizes shows the optimal oxidation resistance both at 1000 °C and 1500 °C. When oxidized at 1000 °C, the formation of a porous oxide layer of Ta2O5, Hf6Ta2O17 and HfO2 containing amorphous SiO2 are primarily responsible for the unsatisfying oxidation resistance of the composite. A highly oxidation resistance component like Si2BC3N can promote the oxidation resistance of Ta4HfC5 at 1500 °C, thanks to the formation of a dense and continuous tantalum-hafnium silicate glass. The oxidation kinetic curve at 1500 °C can be described by a parabolic law whilst the oxidation process is controlled by the diffusion rate of oxygen through the oxide layer; however, the oxidation reaction rate governs the oxidation progress at 1000 °C via a linear oxidation kinetics.

Study of the High‐Temperature Oxidation Behavior of SUS430 Ferritic Stainless Steel Under Different Content of Water Vapor Atmosphere

The oxidation behavior of SUS430 ferritic stainless steel is studied during isothermal oxidation at 1100 °C for 2 h under a mixture of 10, 30, and 50% water vapor and air, and oxidation kinetics curves are drawn. The surface morphology and phase composition of oxide scale are analyzed using X‐Ray diffractometer, scanning electron microscope, and energy dispersive spectrometer. The oxidation kinetic curves under three different humidities are S‐shaped and include three stages: induction period, acceleration period, and deceleration period. The controlling steps under 10% water vapor and air are nucleation and growth, while under 30% and 50% water vapor and air are both phase boundary control reactions. The induction period becomes shorter and the breakaway oxidation occurs earlier with increasing water vapor content. The structure of oxide scale produced is layered, with the outer layer being iron oxide and the inner layer being mainly the Fe–Cr spinel phase. The volatilization of Cr and the growth stress of the Cr2O3 layer cause the formation of nodules, and a large number of cracks are generated in oxide scale. The cracks provide diffusion paths, accelerating the diffusion of Fe ions and electrons, as well as the erosion of the substrate.

Influence of Si addition on the phase structure and oxidation behavior of PVD AlTiN and AlTiCrN coatings using high-resolution characterization techniques

The influence of Si concentrations on AlTiN and AlTiCrN coatings deposited by PVD has been investigated by using high-resolution characterization techniques: TEM, Dynamic SIMS, Atom Probe Tomography (APT) analyses and nano hardness measurements. First, investigations focus on crystallographic phase stability, microstructural observations and micromechanical studies to understand the effect of the Si addition on these two nitride coatings. Second, the oxidation mechanisms and the kinetics of oxide growth at 950 °C for various durations are examined. Results indicate that the addition of Si introduces high compressive stresses in both coating groups, reaching values in the range of − 6 GPa. However, the behavior of Si content differs for AlTiN coatings with and without chromium. In AlTiSiN coatings, increasing Si addition leads to reduce residual stresses, while no significant change is observed for AlTiCrSiN coatings. This stress evolution is associated with a decrease in crystallinity density of the TiAlN coatings due to Si addition, but this structural phenomenon is not observed when Si is added to the quaternary metallic coatings TiAlCrN. Si content also influences the nanohardness, but the variation among coating is not substantial, with values around 34 + /− 2 GPa, and an elastic-modulus around 443 + /− 40 GPa. Regarding oxidation resistance at 950 °C, the addition of Si in AlTiN coating results in the formation of an external alumina oxide layer and beneath it, a nanometer sized TiO2 anatase crystallites layer. After the growth of this bi-layer oxide scale, the inward cationic diffusion of the oxygen is very significantly reduced, and it can explain its high oxidation resistance. In contrast, for AlTiCrSiN coatings, the oxide scale morphology is different, consisting of a pure TiO2rutile outer layer, followed by an Al-rich oxide and a mixed oxide region of (AlCr)2O3 with small islands of TiO2. The growth of this last oxide scale shows a regular increase over time, primarily driven by inward oxygen diffusion at the nitride coating interface.

Microstructure and hot corrosion characteristics evaluation of high-velocity oxy-fuel sprayed Ni–20%Cr coating on AISI 321 steel with Na2SO4–60%V2O5 salt deposits

The high-temperature corrosion is a crucial issue of stainless-steel components such as boilers and superheaters in power plant industries when it operates at elevated temperatures due to impurities in the environment, which deteriorate the properties of the materials. The current research work goal is to investigate the cyclic corrosion characteristics of the bare and Ni–20%Cr, a high-velocity oxy-fuel sprayed coating on AISI 321 steel in Na2SO4–60%V2O5 salt atmosphere at 900 °C. Thermogravimetric study was used to examine the corrosion kinetics by weight change technique. Surface morphology and compositions of the coating and oxide scale morphology were characterized. X-ray diffraction analysis divulges that Fe2O3 is the primary scale in the uncoated specimen. Corrosion attack across the depth and scale thickness is analyzed by a cross-sectional study. More oxide scales spalling could be observed in the uncoated specimen during the corrosion study due to nonprotective Fe2O3 formation. Compared with the bare specimen, the coated steel provides superior corrosion resistance at 900 °C. This is ascribed to the occurrence of NiO, NiCr2O4, and Cr2O3 scales in the coated specimen, which provides sufficient protection to the specimen.

Effect of Ce on microstructure evolution of oxide scale for CLAM steel exposed to LBE containing 10−6 wt% oxygen at 500 ℃

Lead-cooled fast reactor (LFR) is one of the six types of fourth-generation advanced nuclear reactors, and the corrosion with liquid lead-bismuth eutectic (LBE) to structural materials is regarded as a major obstacle restricting the development of LFR. This study focused on the surface morphology of oxide scale, aiming to illustrate the evolution law of oxide scale and the mechanism of Ce effect on oxide scale. China low activation martensitic (CLAM) and Ce-containing CLAM (Ce-CLAM) specimens generated roughly circular and slat-like magnetite islands respectively, but their magnetite pellets had similar growth trends from small to large sizes. Ce delayed the evolution of magnetite, enhanced the adhesion, continuity and integrity of oxide scale for Ce-CLAM specimen. The mechanism model of Ce effect on the evolution of magnetite and the scale growth model of the two kinds of specimens were proposed.

Role of Mn Alloying Element on the Oxide Growth Behavior of 800H Nickel-Based Alloy at 900°C

The addition effect of Mn alloying element on the oxide growth behavior of 800H nickel-based alloy has been study in this paper. The alloy was experienced a cyclic oxidation at 900 °C. The cyclic oxidation test was carried out at oxidizing temperature for one hour followed by cooling at about 200 °C for 20 minutes for each cycle. The test samples were exposed to the cyclic condition up to 150 cycles. The oxidized samples of selected cycles were characterized in term of oxidation kinetic, phase analysis using x-ray diffraction (XRD) spectrometer and oxide scale morphology in plan and cross-sectional view by using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer. As a results, the oxidation kinetic exhibited a weight gain pattern as the exposure cycle increase. Several protective oxide phases which are Cr2O3 and MnCr2O4 oxides were formed. In addition, continuous oxides scale was formed on the sample surface with evidence of Cr-Mn and Cr-rich oxide as detected by EDX analysis.

Oxidation Kinetic and Oxide Scale Morphology of Fe-33Ni-19Cr Ni-Based Superalloy

In the present study, outcome of various grain size of heat treated Fe-33Ni-19Cr Ni-based superalloy at high temperature cyclic oxidation condition was investigated. The Fe-33Ni-19Cr Ni-based superalloy was experienced a series of heat treatment process at two assorted temperatures, which are 1000 °C and 1100 °C, soaking for 3 hours and then rapid cooled by water quench. The heat treatment process produced a fine and coarse grain size structure. The cyclic oxidation test was performed for both heat treated samples at 700 °C under cyclic conditions in the laboratory air for 150 cycles. The weight change was measured discontinuously at different cycles to identify the kinetics of oxidation. SEM and FESEM outfitted with EDX spectrometer were utilized to analyzed the oxidation product. As a result, the weight change increased with time, with fine grain HT1000 sample recorded lower weight gain compared to coarse grain HT1100 sample. In addition, both sample formed uniform and continuous oxide scale on the alloy surface.

The relationship between ignition and oxidation of molten magnesium alloys during the cooling process.

Ignition of magnesium alloys during casting processes limits their processability and applications. For identifying the ignition mechanism of magnesium alloys during solidification, a Mg-Al-Zn alloy was solidified with different cooling rates and pouring temperatures. The oxide scale morphologies and thicknesses were identified by SEM and energy dispersive spectrometer. Based on the experimental results, the oxidation kinetics and heat released were calculated and the relationship between oxidation and ignition was discussed in detail. The calculation results indicate that oxide rupture directly induces combustion of the melt. The rupture route of the oxide scale was determined to be buckling cracks according to the experimental and calculation results. Based on the buckling mechanism of the oxide scale, the ignition criterion during solidification was correlated to the pouring temperature, cooling rate and casting modulus. This work reveals the underlying relationship between ignition and casting process parameters, and it helps to develop new technology for inhibiting ignition of molten magnesium alloys.

Effect of temperature on composition evolution of oxide film on Al–Mg–Sc alloy

The effects of temperature on the component of oxide film on oxidized Al–Mg-Sc alloy surface and the microstructure of Al substrate near the interface were investigated and the relationship between composition change and microstructure evolution was discussed. Results suggested that the morphology of oxide scale evolved from the amorphous oxide layer with dense and uniform structure to the oxide layer with loose structure composed of MgO cluster particles. At 300 °C, the main components of oxide film were Al2O3 and MgO. With the oxidation temperature increasing, MgO gradually made up a major part of the oxide film. When the oxidation temperature reached 500 °C, the major components of the oxide film were MgO and MgAl2O4 and the generation of MgAl2O4 dominated over MgO. With the temperature increasing, the crystal orientation of Al substrate near the interface changed from <101> to <111>, and the transformation of crystal orientation favoured the diffusion of Mg atoms. Meanwhile, the content of high angle grain boundaries (HAGBs) increased significantly, and there were many regions with poor atom matching at the HAGBs, where Mg atoms accelerated the migration to the oxidized Al–Mg-Sc alloy surface to participate in chemical reactions to finally form MgAl2O4 at the interface.

Effects of laser shock processing on θ-Al2O3 to α-Al2O3 transformation and oxide scale morphology evolution in (γ’+β) two-phase Ni-34Al-0.1Dy alloys

• The oxidation resistance of (γ’+β) two-phase NiAlDy alloy is optimized by LSP. • LSP reduces scale growth rate due to its impact on initial oxidation behavior. • LSP promotes θ-α transition by increasing dislocation density and surface roughness. • LSP leads to distinction in oxide scale morphology on both the γ’ and β phase. • LSP facilitates the formation of large Al 2 O 3 particles (2–3 μm) on the β phase. (γ’+β) two-phase Ni-Al is a promising high-temperature protective coating material used on Ni-base superalloys since it has good interfacial compatibility with superalloys due to the low Al content compared to single-phase β-NiAl. In this paper, we aim to improve the oxidation resistance, whereby Ni-34Al-0.1Dy, a (γ’+β) two-phase Ni-Al alloy, was treated by laser shock processing (LSP) and the oxidation behavior at 1150 °C was investigated. The results showed that after oxidation, Al 2 O 3 scale formed on the original β phase of the untreated alloy with a small grain size (200–800 nm), while for the LSP-treated samples, the scale grown on the original β phase was dominantly composed of larger Al 2 O 3 grains with a size of 2–3 μm. The distinction was attributed to the promotion of θ-Al 2 O 3 to α-Al 2 O 3 transformation induced by the LSP, because the dislocation density, as well as surface roughness, were increased during LSP treatment which can provide heterogeneous nucleation sites for α-Al 2 O 3 . In addition, the larger-size Al 2 O 3 particles, derived from the direct conversion of needle-like θ-Al 2 O 3 in the initial oxidation stage, could rapidly overspread the whole β phase surface thus reducing the scale growth rate.

Evaluation of Ni-Fe base alloys as inert anode for low-temperature aluminium electrolysis

• Oxidation behaviors of Ni-Fe-Cr alloys with different Cr content were investigated in air at 800 °C and 900 °C °. • A multilayer oxide structure with an inner Cr 2 O 3 , a middle (Ni,Fe,Cr) 3 O 4 , and an outer (Ni,Fe) 3 O 4 /Fe 2 O 3 layers was formed on Ni-Fe-15Cr alloy. • Increasing of oxidation temperature or Cr content for Ni-Fe-Cr alloys not only accelerates to form Cr 2 O 3 inner layer, but also reduces Fe 2 O 3 content. • The (Ni,Fe) 3 O 4 /(Ni,Fe,Cr) 3 O 4 /Cr 2 O 3 layered scale was highly oxidation/corrosion resistant in molten alumina-cryolite at 800 °C. Isothermal oxidation behaviors of Ni–Fe (wt.%) and of the same alloy with additions of 10 and 15%Cr alloys in the air at 800 °C and 900 °C and their anodic behaviors in aluminum electrolysis system at 800 °C were evaluated. The composition morphologies of oxide scales were characterized by XRD, SEM, and EDS. Results show that the scales formed on Ni–Fe alloy at both temperatures consisted of an inner (Ni,Fe) 3 O 4 layer and an outer Fe 2 O 3 layer. For Ni–Fe–10Cr alloy, an external (Ni,Fe) 3 O 4 /Fe 2 O 3 layers and an internal oxidation zone were formed at 800 °C, while a continuous Cr 2 O 3 layer forms at the internal oxidation zone/substrate interface at 900 °C. A multilayer structure oxide of Cr 2 O 3 /(Ni,Fe,Cr) 3 O 4 /(Ni,Fe) 3 O 4 /Fe 2 O 3 was formed on Ni–Fe–15Cr alloy at 800 °C, while at 900 °C the Fe 2 O 3 becomes discontinuous disperses in the (Ni,Fe) 3 O 4 layer close to the surface. Increases in oxidation temperature or Cr content for Ni–Fe–Cr alloys promote the growth of the inner Cr 2 O 3 layer and simultaneously reduce Fe 2 O 3 content. After 4 h of electrolysis at an anode current density of 0.25 A cm −2 , the oxidation resistance of Ni–Fe–15Cr anode is superior to the Ni–Fe anode.

Isothermal Oxidation Behaviour of 800H Nickel-Based Alloy

The behaviour of 800H nickel (Ni)-based alloy under isothermal oxidation condition was study in this paper. The isothermal oxidation behaviour was examined in terms of fine grained and coarse grained 800H Ni-based alloy obtained from heat treatment operation at 1000 °C and 1150 °C, respectively. The heat treated samples were undergo an isothermal oxidation attempt at 500 °C in laboratory air for 500 hours exposure duration. The effects on the oxidation kinetics was examined in terms of weight change measurement. In addition, the effects on the oxide scale growth was observed in terms of phase analysis using XRD technique and surface morphology analysis using FESEM outfitted with EDX spectrometer. As a results, both fine grained and coarse grained 800H Ni-based alloy were obey a parabolic rate law showing that the oxide growth rate was followed a diffusion controlled mechanism. Additionally, fine grained 800H Ni-based alloy sample exhibited a inferior oxidation rate compared to coarse grained sample. The XRD analysis exhibited that the oxides scale composed of Cr2O3, TiO2 and MnCr2O4. The observation on the oxide scale morphology indicate that uniform oxide scales were formed on the alloy surface of both samples. However, coarse grained 800H Ni-based alloy recorded an oxide exfoliation which indicate poor oxidation protection.

Effect of arsenic on the high temperature oxidation and hot shortness behaviour of copper-bearing steel

To understand the disadvantages caused by As in Cu-bearing steels during hot working processes, high temperature oxidation and surface hot shortness characteristics were systematically investigated using thermogravimetry (TG), optical microscopy (OM), scanning electron microscopy (SEM) and Gleeble-3800 thermal/mechanical simulation system. Analyses of TG curves and the oxide scale morphologies showed that the oxidation kinetics for all steels obeyed the initial linear oxidation law and the later parabolic oxidation law at 950–1050 °C, while the kinetics presented two different stages of the linear oxidation law at 1100 and 1150 °C due to oxide scale separation. Increasing the As content from 0 to 0.15 wt.% decreased the oxidation activation energy and accelerated the oxidation degree of Cu-bearing steel. Cu + As enrichment indicated that an increase in As content induced the precipitation of a more hazardous Cu-rich liquid phase along grain boundaries by decreasing the solubility of Cu in austenite and the melting point of the Cu phase at 1050 °C. Furthermore, the degree of Cu + As enrichment became more serious with an increase in the oxidation temperature from 1000 to 1050 °C, and then decreased because of occlusion and faster back diffusion of Cu + As into the matrix at 1100 and 1150 °C. The hot compression results agreed well with the enrichment behaviour of Cu + As obtained from investigations of isothermal oxidation.

Influence of Water Vapor and Temperature on the Oxide Scale Growth and Alpha-Case Formation in Ti-6Al-4V Alloy

The Ti-6Al-4V alloy is extensively used in aerospace, automotive and biomaterial applications. In the aerospace industry, the service temperature of Ti-6Al-4V is currently limited to 350 °C due to its insufficient oxidation resistance. Oxidation at higher temperatures causes the formation of a fast-growing oxide scale and an oxygen-enriched subsurface layer, which is known as the “alpha-case.” Additionally, the effect of water vapor on the oxidation behavior is critical. In the present study, the oxidation behavior of Ti-6Al-4V in dry air and air containing 10 vol.% H2O at 500, 600 and 700 °C for up to 500 h has been investigated. The main focus of this study is the examination of the different oxide scale morphologies along with the oxygen enrichment in the subsurface zone. It has been observed that spallation of the oxide scale is more severe in a water vapor-containing environment. In dry air, the oxide morphology shows the typical layered TiO2/Al2O3 structure after exposure at 700 °C for 300 h, while Al2O3 precipitates are present in the outermost part of the TiO2 scale when oxidized in wet air. This indicates that the solubility and diffusivity of Al3+ ions in TiO2 are influenced by water vapor. In addition, the extent of oxygen enrichment in the subsurface zone (alpha-case) as a function of temperature and time is determined by nanoindentation profiles. It was shown that in contrast to the scale formation, the alpha-case thickness is not affected by the presence of water vapor in the atmosphere.

Examining oxidation in \u03b2-NiAl and \u03b2-NiAl+Hf alloys by stochastic cellular automata simulations

We present results from a stochastic cellular automata (CA) model developed and employed for examining the oxidation kinetics of NiAl and NiAl+Hf alloys. The rules of the CA model are grounded in diffusion probabilities and basic principles of alloy oxidation. Using this approach, we can model the oxide scale thickness and morphology, specific mass change and oxidation kinetics as well as an approximate estimate of the stress and strains in the oxide scale. Furthermore, we also incorporate Hf in the grain boundaries and observe the “reactive element effect”, where doping with Hf results in a drastic reduction in the oxidation kinetics concomitant with the formation of thin, planar oxide scales. Interestingly, although we find that grain boundaries result in rapid oxidation of the undoped NiAl, they result in a slower-growing oxide and a planar oxide/metal interface when doped with Hf.

Oxide evolution on the SiC layer of TRISO particles during extended air oxidation

Tristructural isotropic (TRISO) fuel particles have been primarily developed for high-temperature gas-cooled nuclear reactors and can be subjected to oxidizing environments for extended periods in an off-normal accident scenario. Surrogate TRISO fuel particles were oxidized in air at 1,000 or 1,100 °C for up to 120 h. The oxide scale morphology and thickness were studied via scanning electron microscopy, focused ion beam, and atomic force microscopy. TRISO particles oxidized at 1,100 °C exhibited a highly crystalline oxide scale, which led to significant cracking and irregularly shaped closed porosity, whereas those oxidized at 1,000 °C possessed a primarily amorphous oxide scale, which contained small, rounded internal pores and no larger defects. The observed phenomena deviated from the expected behavior based on models for oxide growth on flat-plate and fiber SiC. The oxidation kinetics of TRISO fuel particles in high-temperature air were investigated without mechanically deforming the surface and were analyzed with respect to oxide morphology.

Corrosion of Chromia-Forming and Alumina-Forming Ferritic Stainless Steels under Dual Atmosphere Exposure Conditions

The surface morphology and chemistry of oxide scales formed on select chromia-forming and alumina-forming ferritic steels have been studied after exposure to a dual atmosphere of hydrogen and air. Localized Fe-rich oxide nodules with surface whiskers/platelets form at the onset of corrosion. The initiation and growth of localized nodules and breakdown of passivation are attributed to the presence of hydrogen, inclusion of iron oxide in the passivating scale, and subsequent growth of iron-rich oxide due to the establishment of redox (H2-H2O) atmosphere and modification of oxide defect chemistry.

High-temperature oxidation of AlCrFeNi-(Mn or Co) high-entropy alloys: Effect of atmosphere and reactive element addition

The effects of atmosphere (oxygen and steam) and reactive element addition (Zr and Y) on high-temperature oxidation behavior of Al0.5CrFeNiMn and Al0.5CrFeNiCo high-entropy alloys at 1000 °C and 1200 °C were studied. The Al0.5CrFeNiMn alloy displayed different oxidation mechanisms in oxygen and steam owing to differing oxygen partial pressures and preferential oxidation of Mn. A protective alumina scale established on Al0.5CrFeNiCo alloy in both atmospheres and the beneficial effects of Y addition are seen by remarkably improved oxide scale adherence and suppression of convoluted oxide scale morphology. However, doping with 1 wt% Zr deteriorates the oxidation resistance with substantial Al+Zr internal oxidation.