Oxidation Kinetic Curves 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.

Oxidation behavior of 9Cr-RAFM steel at high temperature

The effect of yttrium on the mechanism of oxidation film formation of the 9Cr reduced activation ferritic/martensitic (9Cr-RAFM) steel was investigated. Four alloys yttrium contents ranging from 0 to 0.065% were melted in a vacuum induction furnace and subjected to continuous isothermal oxidation experiments. The alloys were oxidized in air at 600, 700, 800 and 900 °C for 100 h. Oxidation kinetic curves were obtained and analyzed to study the effect of yttrium on the oxidation resistance of the alloys at high temperatures. The oxide films formed on the alloys were observed and analyzed by X-ray diffractometry, scanning electron microscopy and electron probe X-ray microanalysis. The results indicated that the oxidation weight gain of the samples varied with the yttrium content, with the highest gain observed in the yttrium-free alloy sample, and the least in those containing 0.065% yttrium. Adding yttrium significantly enhanced the high temperature oxidation resistance of 9Cr-RAFM alloy by promoting the formation of a selective Cr2O3 oxide film. The film improved the adhesion of the oxide layer to the base metal, reduced the oxidation rate, and thereby enhanced the high-temperature oxidation resistance of the alloy.

Comparison of high temperature oxidation behaviour of high speed steel and Hi-Cr steel

Abstract High speed steel and Hi-Cr steel are widely used as one of the important materials for rolls. The oxide layer during rolling plays a key role in the service life of the rolls and the quality of the rolled material. Therefore, it is very important to study the oxidation behaviour of high speed steel and Hi-Cr steel. In this paper, the oxidation behaviour of HSS and Hi-Cr steel is compared in the range of 500-700°C. The oxidation kinetic curve of HSS is dominated by a parabolic law, while the oxidation kinetic curve of Hi-Cr steel is dominated by a logarithmic law. To analyse the effect of their oxidation products on the oxidation behaviour, V2O5 in high speed steel plays a destructive role in the oxide layer, while Cr2O3 in Hi-Cr steel can effectively reduce the thickness of the oxide layer.

Effect of Sc and Gd co-doping on the oxidation behavior of FeCrAl alloys in water vapor environment at 1000°C

Rare earth Sc, Gd double doped alloys FeCrAl-xScxGd with different compositions (x=0.25, 0.5, 1.0, 2.0) were prepared by vacuum hot press sintering, and their microstructures were investigated. The double-doped alloy FeCrAl-xScxGd was also oxidized with the single-doped alloys FeCrAl-xSc and FeCrAl-xGd (as a control variable) at high temperature water vapor oxidation at 1000 ℃ for 100 h, and the oxidation kinetic curves were investigated. It is concluded that they have positive effects on the enhancement of the oxidation resistance of FeCrAl alloys in different aspects, while there is no "synergistic effect" of Sc and Gd rare earth elements on the oxidation kinetics of FeCrAl alloys. In FeCrAl alloys, the element Gd not only exists as Gd monomer, but also forms two intermetallic compounds of Gd and Fe, Fe5Gd and Fe9Gd, and the oxide Gd3Fe2Al3O12, which hinders the outward diffusion of Al and reduces its oxidation rate. The element Sc, on the other hand, undergoes longitudinal segregation at the oxide grain boundaries and produces a pinning effect on the alumina scale, which enhances the bonding at the oxide scale/alloy interface, thus preventing the growth of new oxide grains and the generation of new nucleation sites at the alumina scale/alloy interface, thus having a positive effect on the alloy.

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.

Microstructure and anti-oxidation behavior of laser clad Ni[sbnd]Si coating on molybdenum surface

Ni-Si alloy coatings with various compositions were fabricated on molybdenum surfaces using laser cladding technology. The sound metallurgical bond without cracks and pores between coatings and substrat was revealed.The microstructure and phase composition of the coatings were analyzed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The oxidation resistance of the coatings was investigated in a static air environment at 700 °C. The results reveal that the coatings primarily consist of a γ-Ni solid solution, Ni3Si phase, and Mo2Ni3Si phase. Furthermore, the Mo2Ni3Si phase content increases with decreasing Ni content in the powder ratio. The oxidation kinetics curve of the NiSi alloy coatings follows a parabolic law. The oxide layer formed on the coating surface is uniform and dense, comprising SiO2, MoO3, and NiMoO4. Based on the comprehensive analysis of the microstructure of the oxide layer, the Ni90Si10 coating demonstrated superior oxidation resistance

Fabrication of yttria-stabilized zirconia/La2O3 composite coating by electrophoretic deposition to improve high-temperature oxidation resistance of stainless steel

Nanoscale yttria-stabilized zirconia (YSZ) and La2O3 were used to prepare a composite coating by electrophoretic deposition (EPD) and sintering to improve the high-temperature oxidation resistance of AISI430 stainless steel. SEM, XRD, and TEM were used to identify the microstructure of the YSZ/La2O3 composite coating and the oxide film formed at 900 °C. The effect of the EPD voltage on the coating thickness was studied. The microstructure properties and phase transition of the composite coatings during sintering were identified. The oxidation behavior of the composite coating at 900 °C was investigated by analyzing the oxidation kinetics curve, oxidation spallation, the formation of the interfacial oxide film, and the evolution of the coating microstructure. A model of the microstructure evolution of the YSZ/La2O3 composite coating during EPD, sintering, and high-temperature oxidation was proposed and discussed.

Steam oxidation properties of graphene reinforced bioinspired laminated CoCrFeNiMn high-entropy alloy matrix composites at 1000 ℃

Laminated CoCrFeNiMn high-entropy alloy (HEA) matrix composites reinforced with 1.0 wt% graphene nanoplatelets (GNPs) were fabricated by mechanical ball milling and flake powder metallurgy, and were isothermal oxidized at 1000 ℃ for 100 h. Vacuum hot-pressure sintering (VHPS) shows a distinct nacre structure with the microstructure composed of FCC matrix phase, Cr23C6, CrMn1.5O4 precipitated phases, numerous dislocations and twins. High-temperature oxidation tests showed that the composites had mass gains at 12 h intervals from 12 to 100 h respectively. The oxidation kinetic curve changes from a linear pattern in the early stages to an exponential pattern in the later stages, which demonstrates better long-term oxidation resistance. The anisotropy of the laminated structure results in excellent resistance to high-temperature steam oxidation in the vertical lamellar direction. Observation of the cross-section reveals that although Cr2O3 (inner layer) is present, (Mn, Cr)3O4 and Mn3O4 are the dominant oxides (outer layer). Elemental depletion zones for Mn and Cr exist in the region of the matrix near the oxide scales. The results show that the oxidation resistance of the laminated GNPs/CoCrFeNiMn composites is mainly influenced by the diffusion of Mn and Cr elements, the microstructure of the laminations and the internal oxidation.

Comparative study on mechanical properties and high temperature oxidation behaviour of Hastelloy X and Inconel 718 fabricated by laser directed energy deposition

The high temperature oxidation resistance is crucial to assure the reliability of nickel-based superalloy parts serving at elevated temperature. Hastelloy X is a solid solution strengthening superalloy featured by decent mechanical properties and excellent high temperature oxidation resistance, having the potential to replace the commonly used nickel-based superalloy Inconel 718 in appropriate high-end manufacturing fields. In this work, a comparative study on mechanical properties and high temperature oxidation behaviour of Hastelloy X and Inconel 718 fabricated by laser directed energy deposition was carried out. Under the same processing parameters, the as-built Hastelloy X consisted of columnar and cellular γ phase with dispersed carbides, but Inconel 718 contained columnar γ phase with dispersed carbides and γ′ phase. At ambient temperature, Hastelloy X showed better ductility but inferior strength and hardness. Additionally, the isothermal oxidation tests at 1000 and 1100 °C demonstrated that the oxidation kinetics curves of both as-built superalloys followed the parabolic law. Hastelloy X owned a better high temperature oxidation resistance, which could be attributed to the uniformly distributed dense Cr2O3 and the relatively slight exfoliation of oxides in the oxide scales.

Surface characteristics and re-ignition law of water-soaked coal in a coal mine closed fire area

There are different degrees of oxidized coal samples in the gobs of coal mines, and there will be hidden dangers of re-ignition of water-soaked coal after the fire zone is closed. Using an atomic force microscope (AFM) and a simultaneous thermal analyzer, the re-ignition properties of coal samples and the pore dynamic evolution in different water-immersed areas of the goaf were studied. The results show that the IO (oxidation after water immersion) coal sample has a more microporous structure and larger fractal dimension when oxidized at 300 °C. The roughness of OI (water immersion after oxidation) coal samples decreases as the oxidation temperature increases. The re-ignition temperature points of the IO300 and O200I coal samples are lower, and the combustion heat release is greater. Before reaching 311 °C, the oxidation kinetics curve conforms to the cubic polynomial ln[-ln(1-a))/T2] =A(1/T)3-B(1/T)2 + C(1/T)-D. After reaching 311 °C, the activation energy of IO300 and O200I coal samples is smaller and more prone to oxidation and re-ignition, which conforms to ln [- ln (1-a))/T2] =A (1/T) – B. Different control measures can be taken in different areas and points based on the oxidized degree and different immersion methods to prevent coal spontaneous combustion (CSC) in closed fire areas.

Effect of Cr content on synergistic effect of Cr-Al during oxidation of high-entropy AlCoCrxNiTi alloys

AlCoCrxNiTi high-entropy alloy coatings, mainly composed of the BCC and B2 phases, were synthesized on Ti-6Al-4V substrates by laser cladding. The incorporation of Cr-refined grains enhanced the hardness of the alloy. Oxidation kinetic curves of the alloys at 800 °C in the air followed the parabolic law, and AlCoCr0.5NiTi alloy exhibited excellent oxidation resistance. The incorporation of an appropriate amount of Cr provided a structural template for the formation of Al2O3 and increased the diffusion rate of Al in the stable oxidation stage, leading to a reduction in the concentration required to form a continuous Al2O3 oxide film.

Effect of Predeformation on the High‐Temperature Oxidation Behavior of 436 Stainless Steel

The effect of a 30% predeformation treatment on the high‐temperature oxidation behavior of 436 stainless steel is investigated by oxidizing it at 900 °C for 100 h in air. After 48 h of oxidation, the undeformed sample primarily exhibits bilayer structures consisting of Cr‐rich oxide and outer Fe oxide, while the predeformed sample predominantly displays a single‐layer structure composed of Cr oxide. The oxidation mechanisms of predeformed and undeformed samples are clarified from the point of recrystallization through oxidation kinetic curves, surface and section micrographs, X‐ray diffraction (XRD), electron probe microanalyzer (EPMA), scanning electron microscope (SEM), energy‐dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD), and line scanning characterization methods. The results show that after 1 h of oxidation, the grain size of the undeformed sample is 34.6 μm, and the grain size of the predeformed sample is 16.0 μm. This reduces the critical content required for the generation of protective Cr oxides and provides more diffusion channels for Cr elements, resulting in the formation of a greater amount of Cr oxides. Cr oxides can inhibit the formation of Fe and Mn oxides, thus delaying the onset of breakaway oxidation and improving its resistance to oxidation.

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.

Effect of coatings on microstructure and oxidation behavior of the Ni-based single crystal superalloys containing different Ru contents

The element Ru in single crystal superalloy usually plays an important role in inhibiting the mutual diffusion between coating and substate. The MCrAlY coating and PtAl coating were prepared on the fourth and third generation single crystal superalloy, and the isothermal oxidation behaviors of the two superalloys and the two coatings were investigated in static laboratary air at 1200 °C. The oxidation kinetic curves showed that the mass gain of the coated samples was less than the alloys without coatings, which meant the coatings showed more excellent oxidation resistance at high temperature, and the oxidation resistance of the two coatings was slightly enhanced by the addition of Ru during the oxidation tests. Meanwhile, the interdiffusion of elements, such as Al in coating and refractory elements in substrate, was hindered by the addition of ruthenium. The size of γ' phase was also inhibited. As a result, the formation of interdiffusion zone and the precipitation of topological-close packed phase were suppressed, resulting that the DD91 showed more stable microstructure at elevated temperature than the DD90 during the oxidation process. The advantage of Ru in the alloys with coatings will be discussed in detail as well as the protective performance of coatings.

Distinctive performance evolution of surface layer in TC4 alloy oxidized at high temperature: Softening or hardening?

The characteristics of metal surface layer at high-temperature significantly affect the service performance of TC4 titanium alloy components, so that the evolution mechanism of mechanical properties of metal surface layer under high-temperature oxidation conditions is an important scientific issue. In the present work, the mechanical behavior and the relevant mechanism of metal surface oxidized at the temperatures of 500 ℃, 700 ℃, and 900 ℃ for different times have been systematically investigated. The experimental results show that with the increase of temperature, the oxidation kinetics curve of the alloy changes from parabolic law to linear law, and the oxidation reaction changes from diffusion control to interfacial reaction control. Furthermore, as the temperature increases from 500 °C to 900 °C, the feature of oxide scale changes from the single-layer structure to the multi-layer alternating structure, and the thickness of oxide scales and depth of alpha case increased with increasing temperature. The surface oxide scale is mainly composed of low valent oxides such as Ti3O and Ti6O during low-temperature oxidation as well as short-term high temperature oxidation. After long-term high temperature oxidation, the oxide scale is mainly composed of high valent oxides such as TiO2, Al2O3, and TiVO4. Simultaneously, significant changes occur in the composition, microstructure and properties of metal surface layer. In general, the microstructure and mechanical properties of the surface-layer metal are strongly dependent upon the competitive influence of the outward diffusion of Al and the inward diffusion of O. In the temperature range of 500–900ºC, when the temperature is relatively low, the softening effect caused by the outward diffusion of Al is stronger than the strengthening effect caused by the inward diffusion of O, and a surface softening effect thus occurs. On the contrary, when the temperature is high, the strengthening effect caused by the inward diffusion of O is stronger than the softening effect caused by the outward diffusion of Al, and a surface strengthening effect accordingly happens.

Effect of refractory element addition on high temperature oxidation process of complex concentrated alloy coatings

The sluggish diffusion effect of complex concentrated alloys (CCAs) affords them considerable application potential in the field of high temperatures. In this study, the role of refractory elements in the high temperature oxidation process of denary complex concentrated alloy coatings (CCACs, namely NiCoCrFeAl0.8Si0.1(MoNbTaW)x, where x is 0.025, 0.05, 0.1 and 0.15) prepared via laser cladding was investigated. Four groups of the CCACs with different refractory contents were subjected to 100 h of high-temperature oxidation experiments, and the oxidation products and microscopic characteristics of the samples were observed via XRD and SEM, respectively. Atomic-scale characterisation and analysis of the oxidised samples were performed using TEM and XPS technology to explore the diffusion behaviour of elements in the high-temperature process. Results indicate that the solid solution limit of the CCACs is obtained by regulating the topological instability of the lattice matrix via the addition of refractory elements. Consequently, when 0.1 > x > 0.025, the coating is a body-centred cubic (BCC) + face-centred cubic (FCC); when x = 0.1, the coating maintains a single-phase FCC structure; and when x > 0.1, the coating changes to an FCC + BCC duplex structure. The x0.1 group exhibits the smallest relative strain among all coatings, which is conducive to maintaining the structural stability of the face-centred cubic at high temperatures and delaying atomic migration within the lattice. Furthermore, the oxidation kinetics curve of the CCACs with a single- phase FCC exhibits low Kp values. In a single- FCC lattice, the atom diffusion rate through volume slows down and grain boundary diffusion decreases. Considering the Weibull modulus for the hardness statistical value after coating oxidation, the modulus of single-FCC phase CCACs is also higher than others. This study has the potential to contribute to the application of high-temperature thermal protection for CCACs.

The failure behavior of thermally grown oxide of the AlCoCrFeNi bond coating prepared by atmospheric plasma spray at 900–1000 °C

The AlCoCrFeNi high entropy alloy bond coating was prepared by atmospheric plasma spray. The growth process and failure behavior of the thermally grown oxide (TGO) layer during the oxidation of the AlCoCrFeNi bond coating at 900–1000 °C were investigated. Results show that the AlCoCrFeNi bond coating generates a protective TGO layer composed of Al2O3 at 900–1000 °C, which effectively reduces the oxidation rate of the coating. The oxidation kinetic curves of the AlCoCrFeNi coating at 900–1000 °C exhibited a parabolic pattern. Until 50h oxidation, the TGO layer at 900 °C remained complete. In contrast, the TGO layer exfoliated at 1000 °C, associated with the thermal mismatch stress between the TGO layer and the AlCoCrFeNi coating. The growth of the TGO layer is primarily controlled by the outward diffusion of Al ions, which causes the generation of Al ion vacancies within the coating, consequently developing into visible pores. The presence of pores exacerbates the possibility of TGO layer exfoliation. The control of the outward diffusion process of Al ions, which can reduce the growth rate of the TGO layer and the amount of pores in the coating, is an important idea to improve the oxidation resistance of AlCoCrFeNi coating.

Fabrication and Oxidation Resistance of a Novel MoSi2-ZrB2-Based Coating on Mo-Based Alloy.

To enhance the oxidation resistance of Mo-based TZM alloy (Mo-0.5Ti-0.1Zr-0.02C, wt%), a novel MoSi2-ZrB2 composite coating was applied on the TZM substrate by a two-step process comprising the in situ reaction of Mo, Zr, and B4C to form a ZrB2-MoB pre-layer followed by pack siliconizing. The as-packed coating was composed of a multi-layer structure, consisting of a MoB diffusion layer, an MoSi2-ZrB2 inner layer, and an outer layer of mixture of MoSi2 and Al2O3. The composite coating could provide excellent oxidation-resistant protection for the TZM alloy at 1600 °C. The oxidation kinetic curve of the composite coating followed the parabolic rule, and the weight gain of the coated sample after 20 h of oxidation at 1600 °C was only 5.24 mg/cm2. During oxidation, a dense and continuous SiO2-baed oxide scale embedded with ZrO2 and ZrSiO4 particles showing high thermal stability and low oxygen permeability could be formed on the surface of the coating by oxidation of MoSi2 and ZrB2, which could hinder the inward diffusion of oxygen at high temperatures. Concurrently, the MoB inner diffusion layer played an important role in hindering the diffusion of Si inward with regard to the TZM alloy and could retard the degradation of MoSi2, which could also improve the long life of the coating.

The oxidation behavior of a ductile Hf0.5Nb0.5Ta0.5Ti1.5Zr refractory high-entropy alloy in pure oxygen condition at 500–900 °C

In this study, the oxidation behavior of Hf0.5Nb0.5Ta0.5Ti1.5Zr refractory high-entropy alloy (RHEA) was investigated at temperature range of 500–900 °C in pure oxygen condition, and the oxidation mechanism was systemically discussed. The oxidation kinetics curve shows linear lines with the initially slow and subsequently faster oxidation rate at 700 °C. As the oxidation temperature increased to 800 °C, the oxidation curve comprises three stages: beginning linear lines, intermediate breakaway platform and final parabola. In addition, the oxidation kinetics curves exhibit near parabolic in all the studied temperature. The oxygen diffusion was considered as the predominant mechanism in the oxidation of RHEA.

Oxidation Property of a Fourth-Generation Powder Metallurgy FGH4108 Nickel-Based Superalloy

Isothermal oxidation kinetics of a fourth-generation powder metallurgy FGH4108 nickel-based superalloy is investigated at 800 °C to 1100 °C by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). At 800 °C and 900 °C, the oxidation kinetic curves of the FGH4108 superalloy follow parabolic law. At 1000 °C, the oxidation kinetic curve follows cubic law. At 1100 °C, the oxidation kinetic curve has two distinct parts: the first part follows a parabolic law, and the second one obeys a linear law. Cross-sectional morphologies and elemental distributions show that the oxide film consists of two parts at 800 °C: the outer layer is a continuous dense protective Cr2O3 oxide film, and the inner layer is a discontinuous Al2O3 oxide layer. At 900–1100 °C, the oxides consist of three layers: the outermost is the oxides of Cr2O3 and TiO2, the middle is a continuous oxide of Al2O3, and the innermost is dotted oxides of TiO2. The thickness of the inner TiO2 oxide layer increases with the increase of oxidation temperature. On this basis, the oxidation behavior of the FGH4108 superalloy at high temperatures is confirmed to be controlled by the diffusion of Cr, Al, Ti, and O. From the aspect of oxidation resistance, the long-term service temperature of the FGH4108 superalloy should not exceed 1000 °C.