Mechanism Of High-temperature Oxidation Research Articles

The high-temperature oxidation behavior and mechanism in a powder metallurgy Ni-based superalloy featuring δ-Nb3Al addition

The high-temperature oxidation behavior and mechanism in a powder metallurgy Ni-based superalloy featuring δ-Nb3Al addition

Effect of Microstructure on Oxidation and Micro-mechanical Behavior of Arc Consolidated Mo-Ti-Si-(B) Alloys

AbstractThe present study deals with the development and characterization of Mo-35Ti-10Si and Mo-35Ti-10Si-2B (wt.%) alloy for ultra-high temperature applications beyond the temperature limit of existing super alloys. The microstructural characterization using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), electron back scattered diffraction (EBSD), x-ray diffraction (XRD) revealed that the Mo-35Ti-10Si-2B alloy was consisted of three phases, namely, (Mo, Ti)ss, (Mo, Ti)5SiB2 and (Ti, Mo)5Si3; whereas, Mo-35Ti-10Si alloy was found to be consisting of (Mo, Ti)ss, and (Mo,Ti)3Si phases. Since quantification of boron is difficult by EDS, Particle Induced Gamma-ray Emission (PIGE), a nuclear reaction analysis technique was used for chemical composition analysis of boron. The oxidation behavior of the Mo-35Ti-10Si-2B alloy in the temperature regime of 825-1250 °C was studied in detail and compared with boron-free Mo-35Ti-10Si alloy. Mo-35Ti-10Si-2B alloy exhibited superior oxidation behavior at intermediate temperatures of 825 °C, and excellent oxidation resistance at higher temperatures between 1000 and 1250 °C due to the formation of the protective borosilica and double oxide layers (TiO2 and duplex borosilica-TiO2), respectively. High-temperature oxidation mechanisms were discussed using detailed microstructural cross section analysis of the oxidized alloy samples. The micro-mechanical behavior of constitutive phases of the Mo-35Ti-10Si-2B alloy were studied by microhardness, nano-indentation and micropillar compression testing. The micropillar compression of (Mo, Ti)ss phase showed fairly ductile behavior with the evidence of activation of dislocation in the form of slip lines revealed through the post-deformation fractography. Deformation studies of (Mo, Ti)5SiB2 and (Ti, Mo)5Si3 phases were also carried out which showed large strain bursts indicating possibility of activation of dislocation activities even at room temperatures imparting low level of ductility.

Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2

Transition metal silicides represented by MoSi2 have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi2 oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi2 at temperatures of 1000 °C–1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi2 underwent high-temperature selective oxidation reactions at 1000 °C–1200 °C, forming MoO2 and SiO2 oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO2 and the phase transformation of SiO2, a continuous Mo5Si3 layer with a thickness of approximately 47 μm was formed at the SiO2–MoSi2 interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO2 and Mo5Si3) during high-temperature oxidation process of MoSi2. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo5Si3 layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi2 coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo5Si3 during the high-temperature oxidation of MoSi2 coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.

High-temperature oxidation mechanism and microstructure evolution of Cr-Mn-Si alloyed steel oxidized by Fe2O3 contained in mold flux

The high-temperature oxidation behavior of Cr-Mn-Si alloyed steel by Fe2O3 contained mold flux in high temperatures, and its effect on microstructure evolution were investigated in detail by TEM, EBSD, CLSM, SEM, and XPS. A novel oxidation mechanism was firstly revealed that the Fe2O3 in mold flux melts during high temperatures plays a role of oxidizing alloyed steels by the released free oxygen ions (O2−) from the transformation of Fe2O3 (Fe3+) to FeO (Fe2+). The formed oxidized dots within the oxide layer changed from SiO2 and MnSiO3 to MnCr2O4 spinel phases by increasing the content of Fe2O3 in the mold flux. Notably, the amorphous SiO2 was discovered in the core region of MnSiO3 phase due to its selective oxidative behavior in high temperatures. This research provides conclusive evidence that the small size MnSiO3 oxides can be acted as a nucleation core for the refinement of austenite grains through in-situ observation.

Understanding the high-temperature oxidation resistance of heat-resistant austenitic stainless steel with gradient nanostructure

The underlying high-temperature oxidation mechanisms of the heat-resistant austenitic stainless steel with gradient nanostructured surface layer is revealed through systematic analysis of the microstructure and composition. Nanoscale oxide grains and high-density grain boundaries promoted the formation of pronounced spinel oxides, which suppressed elemental diffusion and CrO3 volatilization. High level of residual stress in the GNS layer facilitated the formation of high-density precipitates at the oxide/matrix interface and grain boundaries, which hindered the growth of oxide scale and reactive elements diffusion. The enhanced high-temperature oxidation resistance resulted from the synergistic combination of spinel oxides, precipitates, and high-density grain boundaries.

Investigation on the high-temperature oxidation behavior and mechanism of laser-cladded Inconel625 coating at various temperatures

This study examines the high-temperature oxidation behavior of laser-clad Inconel 625 coatings under different temperature and time conditions. The coating's microstructure, compositional elements, and oxidation products have been characterized through various analytical methods, including Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), and Laser Confocal Microscopy. The experimental results showed that as the temperature increased in the isothermal oxidation process, the mass of the coatings increased, and the mass gain followed a parabolic relationship with oxidation time. The rate constant exhibited an exponential relationship with temperature. Both oxidation time and temperature had significant effects on the composition and formation of the oxide layer. At lower temperatures, the oxidation process is slow, with an oxidation weight gain of approximately 0.00053 mg/cm2. However, above 600 °C, the oxidation films began to form rapidly, increasing by 0.0169 mg/cm2. Moreover, as the temperature rose, different types of oxides formed at various temperature regimes. At 800 °C, the oxidation film had a thickness of approximately 3.75 μm and a weight gain of 1.19921 mg/cm2. At this point, oxides such as Cr2O3, Nb2O5, NiO, and spinel NiCr2O4 appeared. When the temperature reached 1000 °C, the oxidation film expanded to approximately 63.88 μm in thickness, with a weight gain of 3.5326 mg/cm2. The oxidation products at this temperature were Cr3O4 and spinels NiCr2O4, CrNbO4, NiNb2O6. These findings contribute valuable insights for understanding the dynamic behavior and assessing the service life of laser-clad nickel-based alloy coatings subjected to high-temperature oxidation corrosion.

Correction: High-Temperature Oxidation and Hot Corrosion Behaviors and Mechanism of One Typical Aero-Engine Material 0Cr18Ni9 by One Novel Superhydrophobic and Oleophobic Ultrafine Dry Powder Extinguishing Agent

Correction: High-Temperature Oxidation and Hot Corrosion Behaviors and Mechanism of One Typical Aero-Engine Material 0Cr18Ni9 by One Novel Superhydrophobic and Oleophobic Ultrafine Dry Powder Extinguishing Agent

Electronic-scale assessment of high-temperature oxidation mechanisms in a novel Fe-based alloy

Electronic-scale assessment of high-temperature oxidation mechanisms in a novel Fe-based alloy

Effect of Silica Nanofiller on Thermal-Oxidative Degradation of Epoxy Composites Synthesized by the Sol-Gel Method

Using the sol-gel method, amine-curing polymer silica composites based on cycloaliphatic epoxy resin were obtained. The content of SiO2 filler in the composites was 0.5–10 wt %. The formed mass fractal of silica nanoparticles during the synthesis of composites has a reinforcing effect on the epoxy polymer matrix. The patterns of non-isothermal destruction of polymers and composites in the presence of atmospheric oxygen have been established. At 5 wt % SiO2, the effective activation energy of the main stage of destruction of composites increases from 165 to 254 kJ mol–1. As a result, the rate of weight loss of the samples decreases (the temperature corresponding to 50% weight loss shifts towards higher values by 30°C). The mechanism of high-temperature oxidation of pure polymer and composite with oxygen has been studied. It has been established that the introduction of SiO2 into the composition of composites increases the activation energy of isothermal oxidation of the substrate.

High-Temperature Oxidation and Hot Corrosion Behaviors and Mechanism of One Typical Aero-Engine Material 0Cr18Ni9 by One Novel Superhydrophobic and Oleophobic Ultrafine Dry Powder Extinguishing Agent

High-Temperature Oxidation and Hot Corrosion Behaviors and Mechanism of One Typical Aero-Engine Material 0Cr18Ni9 by One Novel Superhydrophobic and Oleophobic Ultrafine Dry Powder Extinguishing Agent

Microstructure, high-temperature corrosion resistance and oxidation properties of (TiVZrCrAl)N high entropy nitride coatings with different N2/Ar ratios

The (TiVZrCrAl)N high-entropy nitride coatings were prepared on Zr-4 alloy substrates by reactive magnetron sputtering with different N2/Ar pressure ratios I values. The microstructure, nanohardness, high-temperature corrosion and steam oxidation resistance properties of the coatings were investigated. The results showed that the thickness of the coating first decreaseds and then increaseds with decreasing N2/Ar pressure ratio, but the hardness first increaseds and then decreaseds. All the coatings exhibited B1-NaCl structure. When I = 1/12, the (TiVZrCrAl)N coating had excellent high-temperature corrosion resistance and steam oxidation performance. The high-temperature steam oxidation mechanisms of the (TiVZrCrAl)N coatings were analyzed in detail.

Exceptional high-temperature oxidation resistance and mechanisms of a novel chemically complex intermetallic alloy

A novel chemically complex intermetallic alloy (CCIMA) dominated with an ordered L12 structure was designed based on the multicomponent Ni-Co-Cr-Al-Mo-Ti-Ta-Nb-B system. Its oxidation behaviors and underlying mechanisms were systematically investigated. Oxidation at 900 ℃ and 1000 ℃ results in the formation of main multicomponent spinel oxides in the outmost layer, spinel oxides containing rutile-type oxides and boron oxides in the intermediate layer, and continuous Al2O3 in the inner layer. Furthermore, oxidation leads to phase transformation from L12 to D024 at the matrix/oxide layer interface due to Al-depletion. The continuously formed inner Al2O3 oxides have well protected the alloy from oxidizing.

The role of (Fe,Al)2Nb Laves phase on the high temperature oxidation behaviour of intermetallic Fe–26Al–4Nb iron aluminide

The role of the (Fe,Al)2Nb Laves phase on the high temperature oxidation mechanisms of Fe–26Al–4Nb (at%) was investigated between 700 °C and 1000 °C in air for 500 h. The (Fe,Al)2Nb Laves phase that was already present in as-cast state was selectively oxidised at all temperatures but showed the formation of different oxides including Fe2O3, AlNbO4, and Al-rich oxide depending on test temperature. Unharmed (Fe,Al)2Nb was newly formed below the oxide scale at 700 °C and 800 °C, while at 900 °C and 1000 °C no unharmed Laves phase below the oxide layer was observed. The discontinuous isothermal testing showed a change of kinetics at 700 °C and 800 °C after 10 h of oxidation. At 1000 °C, the (Fe,Al)2Nb Laves phase was additionally identified to initiate oxide spallation.

Influence of Cr Content on the High-Temperature Oxidation Behavior and Mechanism of Low-Alloy Steels.

The high-temperature oxidation behavior of low-carbon steel (AISI 1015, AISI 8617, AISI 4115) was investigated over the temperature range from 600 to 1000 °C in humid air containing 25% water vapor. Mass gain of oxidation measurement was performed to study the oxidation kinetics. The microstructure, thickness, and composition of the oxide scale formed were investigated via optical microscope (OM), scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and electron probe microanalyzer (EPMA). The oxidation process was performed from 2 to 100 min. As the oxidation time increased, the trend of mass gain per unit area switched from a linear to a parabolic law, regardless of the steel grade used. As the chromium content increased, the duration of time during which the oxidation rate followed a linear relationship decreased. In the low-alloy steel with higher chromium content, the thickness of the mixed oxide layer containing Cr increased and the oxidation rate decreased at all oxidation temperatures.

High temperature oxidation behavior of porous MoAlB ceramic from 800 °C to 1100 °C in air

MoAlB possesses the characteristics of both metals and ceramic materials, which has attracted extensive attention due to its excellent high-temperature oxidation resistance. For this reason, porous MoAlB is considered applicable to the practice of filtration under harsh environment. In this study, the high-temperature oxidation behavior of porous MoAlB ceramics is systematically studied at the temperatures ranging from 800 to 1100 °C. According to the results, the porous MoAlB exhibits good oxidation resistance at a maximum temperature of 1000 °C. The oxidation kinetics of porous MoAlB can be divided into three stages, and the estimated activation energies of the three stages are 253.83 kJ·mol−1, 367.48 kJ·mol−1 and 317.84 kJ·mol−1, respectively. In the stable stage at 1000 °C, the quadratic mass gain per unit area shows linearity over time, and the oxidation rate of porous MoAlB reaches 37.31 mg2·cm−4·h−1. As revealed by the analysis of the composition and microstructure of oxide layers, the main components of the oxide layer include MoO3, MoO2, Al2O3, B2O3. With the extension of oxidation time, the content of Al2O3 in the oxide films increases. The average pore size, permeability and open pore porosity of porous MoAlB show a trend of first decreasing and then tending to be stable. In addition, a discussion is conducted on the high-temperature oxidation mechanism of porous MoAlB.

Mechanism and kinetics of high-temperature oxidation of medium- and high-entropy carbides in air

Medium- and high-entropy carbides (MECs and HECs) have a wide range of advanced applications and, in many cases, outperform monocarbides. However, the behavior, oxidation mechanisms, and factors defining oxidation resistance of some popular HECs at high temperatures have not been studied in detail yet. In this study, the oxidation behavior of MEC and HECs including (Ta,Ti,Nb,Zr)C, (Ta,Ti,Nb,Zr,Mo)C, (Ta,Ti,Nb,Zr,Hf)C, and (Ta,Ti,Nb,Zr,W)C was investigated under both non-isothermal and isothermal conditions at temperatures up to 1200 °C, and a possible oxidation path was described. It was found that under non-isothermal heating conditions, the oxidation of HECs occurred in three stages, each governed by first-order chemical reactions, and was limited by the formation of ZrO2, Me2Me6O17, and MeMe2O7 oxides, respectively. In the case of isothermal heating, the oxidation of (Ta,Ti,Nb,Zr)C, (Ta,Ti,Nb,Zr,Mo)C, and (Ta,Ti,Nb,Zr,Hf)C follows a logarithmic law and was limited by the formation of a protective Me2Me6O17 layer. In contrast, isothermal oxidation of (Ta,Ti,Nb,Zr,W)C followed a linear law due to the formation of volatile WO3. The results of the study have a high potential for practical application for the production of HEC ceramics for various high-temperature purposes and could be used for further understanding of functional characteristics and development of the new ceramic compositions.

Kinetic modeling of NH3-selective catalytic reduction (SCR) over a mildly hydrothermally aged commercial Cu-SSZ-13 catalyst

Cu-SSZ-13 is often studied as a selective catalytic reduction (SCR) of NOx catalyst for diesel after-treatment systems. Mild hydrothermal aging (HTA) is commonly known to cause changes in catalyst performance. In this study, a kinetic model of SCR over a Cu-SSZ-13 catalyst that includes mild HTA and its impact on the SCR reaction was developed. The migration of Cu species during HTA, and how this change in Cu distribution affects low-temperature and high-temperature NH3 oxidation and SCR reaction mechanisms, were considered. Flow reactor test results were used for parameter estimation and verification. Different characterization techniques, including H2 temperature-programmed reduction (H2-TPR), NO + NH3-TPR, NH3 temperature-programmed desorption (NH3-TPD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), were used to characterize and quantify catalyst site densities. The model can simulate the migration of Cu species and the NOx reduction performance changes during mild hydrothermal aging as a function of aging temperature and time.

High-temperature oxidation properties of economical and lightweight Fe-Cr-Ni-Al medium-entropy alloy

This study investigated the microstructure, high-temperature oxidation properties and mechanism of non-equiatomic Fe-Cr-Ni-Al medium entropy alloy (MEA). Microstructural observation of MEA identified coarse grains of mm scale, and cuboidal precipitates with an average size of 125 nm were evenly distributed within grains. Phase analysis confirmed that the alloy consisted of a Fe-Cr matrix (BCC structure) and B2 Ni-Al precipitate. High temperature isothermal oxidation tests measured oxidation weight of 0.08 mg/cm2 at 800 ℃, 0.17 mg/cm2 at 900 ℃, 0.22 mg/cm2 at 1000 ℃, and 0.47 mg/cm2 at 1100 ℃. Compared to other alloys tested with similar conditions, Fe-Cr-Ni-Al MEA presented by this study achieves economic benefits with relatively excellent high-temperature oxidation resistance. The outstanding high-temperature oxidation resistance of the MEA presented by this study is due to the evenly distributed dense stable Al2O3 layer formed regardless of temperature conditions. In addition, the alloy did not have breakaway oxidation, which can occur as oxidation progresses.

The Effect of Dopants on Structure Formation and Properties of Cast SHS Alloys Based on Nickel Monoaluminide.

Alloys based on NiAl-Cr-Co (base) with complex dopants (base+2.5Mo-0.5Re-0.5Ta, base+2.5Mo-1.5Re-1.5Ta, base+2.5Mo-1.5Ta-1.5La-0.5Ru, base+2.5Mo-1.5Re-1.5Ta-0.2Ti, base+2.5Mo-1.5Re-1.5Ta-0.2Zr) were fabricated by centrifugal SHS metallurgy. The phase and impurity compositions, structure, mechanical properties, and the mechanism of high-temperature oxidation at T = 1150 °C were studied; the kinetic oxidation curves, fitting equations and parabolic rate constant were plotted. Al2O3 and Co2CrO4 were the major phases of the oxidized layer. Three layers were formed: I-the continuous Al2O3 layer with Co2CrO4 inclusions; II-the transitional MeN-Me layer with AlN inclusions; and III-the metal layer with AlN inclusions. The positive effect of thermo-vacuum treatment (TVT) on high-temperature oxidation resistance of the alloy was observed. The total weight gain by the samples after oxidative annealing decreased threefold (from 120 ± 5 g/m2 to 40 ± 5 g/m2). The phases containing Ru and Ti microdopants, which reduced the content of dissolved nitrogen and oxygen in the intermetallic phase to the values ∑O, N = 0.0145 wt.% for the base+2.5Mo-1.5Ta-1.5La-0.5Ru alloy and ∑O,N = 0.0223 wt.% for the base+2.5Mo-1.5Re-1.5Ta-0.2Ti alloy, were identified by transmission electron microscopy (TEM). In addition, with the significant high-temperature oxidation resistance, the latter alloy with Ti had the optimal combination of mechanical properties (σucs = 1644 ± 30 MPa; σys = 1518 ± 25 MPa).

Effects of Ta and Y additions on the high temperature oxidation mechanisms of Ni–10Al alloy at 1100 °C

Ni–10Al-xTa (x = 0, 0.4, 1, 3 wt%) and Ni–10Al-0.4Ta-xY (x = 0.2, 0.4, 0.6 wt%) alloys were prepared by powder metallurgy technology. The effect of Ta and Y on the oxidation resistance mechanism of Ni–10Al alloy at 1100 °C was investigated. The results show that Ta forms Ta-rich regions (including Ni3Ta and Ta oxides) in the alloy matrix. Ta-rich regions on the surface become preferential sites to produce poorly protected NiTa2O6. However, the Ni3Ta in the matrix beneath the oxide film hinders the outward diffusion of Al, reducing the consumption of Al and enhancing the stability of Al2O3 layer. The conflicting effect of Ta allows for a range of Ta additions. The oxidation resistance of Ni–10Al alloy is improved with minor Ta (0.4 wt%) and excess Ta destroys the oxide film. The minor Y addition (0.2 wt%) promotes the adhesion of oxide film, while excessive Y accelerates the production of NiO and the internal oxidation of Al2O3, resulting in an increased oxidation rate. In addition, Y impedes the outward diffusion of Ta, which inhibits the production of NiTa2O6 and Ta oxides in the oxide film.