High Temperature Oxidation Research Articles

Synthesis and reaction mechanism of high injected electron concentration and low work function [Ca24Al28O64]4+:(4e-) by Sol-gel method combined with spark plasma sintering

The high injected electron concentration and low work function C12A7:e- was successfully prepared by the sol-gel method combined with spark plasma sintering(SPS) using calcium nitrate, aluminum nitrate, citric acid, and ethylene glycol as raw materials. By analyzing the morphology of carbon and its role in the reactive synthesis, we reveal the reaction synthesis mechanism of C12A7:e- under the SPS. The analysis shows that C12A7:e- started to be generated at 800 °C. During the SPS reaction sintering process, carbon atoms from citric acid and ethylene glycol were excited by a pulsed current at high temperature, forming the carbon ions C22- and C (gas). Both act as reducing agents and react with the free oxygen ions O2- in the C12A7 cage cavity to form gaseous CO or CO2, enabling electrons to be injected into the cage cavity, thus generating C12A7:e-. Meanwhile, the graphene oxide (GO) formed on the surface of C12A7:e- grain is produced by the precursor of sol-gel synthesis in the high temperature oxidation environment, which will be conducive to improving the stability of C12A7: e- in air and high temperature oxidation resistance.

Preparation and high temperature oxidation resistance of AlSiY coating by arc ion plating

AlSiY coating with excellent antioxidant property was deposited using the arc ion plating technique on a nickel-base single crystal superalloy René N5. The microstructures and morphologies of the coatings, the elemental content and composition of the phases were analyzed by scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS), and X-ray diffractometer (XRD). The results showed that the AlSiY coating was primarily comprised with β-NiAl phase with well combined with the substrate after heat treatment. The average oxidation rate of the coating for 300 h oxidation at 1050 ℃ was 0.8570 mg/cm2, superior to that of the substrate with 1.0035 mg/cm2. The coating exhibited good resistance oxidation during 1050 ℃, and the main phase was β-NiAl phase with high Al content after 300 h oxidation, which suggested that the coating could form a dense Al2O3 layer. In the 1100 ℃ oxidation process, although the depleted aluminum zone of γ′-Ni3Al was formed under the oxide layer after 300 h oxidation, the coating still had a high Al content, which could generate a continuous oxide layer on the surface of coating. The average oxidation rate of coating and substrate was 1.4070 mg/cm2, 3.2730 mg/cm2, respectively, which could provide good oxidation resistance for substrate. The investigation could provide some guidance for the preparation and industrial production of aluminide coatings.

Microstructural evolution and high-temperature oxidation behavior of plasma sprayed SiC-YSZ TBCs

In this work, the effect of SiC addition on the microstructure, porosity, phase composition, weight gain, and thickness of TGO of the coatings after repeated oxidation at 1300 °C for various time of APS SiC-YSZ TBCs have been investigated. The phase of the as-sprayed coatings is consisted of t’-ZrO2, SiC and very little SiO2. With the increase of SiC addition, the diffraction peak intensity of SiC and SiO2 are both increased. SiC and SiO2 can fill into the pores in YSZ effectively. However, the porosity in the coatings has little changed with the increased of SiC addition. The addition of SiC during repeated oxidation at 1300 °C can limit the development of the m-ZrO2 phase while causing no ZrO2 lattice deformation. Increasing the SiC addition can impede the growth of TGO between the bonding layer and the ceramic layer, lowering the thermal weight gain rate of the SiC-YSZ coating. The lowest thermal weight gain rate occurs when the SiC composite concentration is 15 wt%. When the composite content of SiC is increased by 10 wt%, the percentage of O element at the interface between the bonding layer and the ceramic layer decreases by approximately 6.56 wt%. Increasing the SiC concentration will improve the compactness of the interface between the bonding and ceramic layers, and limit grain formation in the bonding layer. However, the SiC composite composition must match the ceramic coating's porosity. When the SiC percentage is too low, the ceramic layer's porosity increases and TGO development accelerates. When the SiC concentration is too high, it agglomerates and connects within the coating, causing the coating to fail off during high temperature service.

High-Temperature Oxidation and Phase Stability of AlCrCoFeNi High Entropy Alloy: Insights from In Situ HT-XRD and Thermodynamic Calculations.

The high-temperature oxidation behaviour and phase stability of equi-atomic high entropy AlCrCoFeNi alloy (HEA) were studied using in situ high-temperature X-ray diffraction (HTXRD) combined with ThermoCalc thermodynamic calculation. HTXRD analyses reveal the formation of B2, BCC, Sigma and FCC, phases at different temperatures, with significant phase transitions observed at intermediate temperatures from 600 °C-100 °C. ThermoCalc predicted phase diagram closely matched with in situ HTXRD findings highlighting minor differences in phase transformation temperature. ThermoCalc predictions of oxides provide insights into the formation of stable oxide phases, predominantly spinel-type oxides, at high p(O2), while a lower volume of halite was predicted, and minor increase observed with increasing temperature. The oxidation behaviour was strongly dependent on the environment, with the vacuum condition favouring the formation of a thin, Al2O3 protective layer, while in atmospheric conditions a thick, double-layered oxide scale of Al2O3 and Cr2O3 formed. The formation of oxide scale was determined by selective oxidation of Al and Cr, as further confirmed by EDX analysis. The formation of thick oxide in air environment resulted in a thick layer of Al-depleted FFC phase. This comprehensive study explains the high-temperature phase stability and time-temperature-dependent oxidation mechanisms of AlCrCoFeNi HEA. The interplay between surface phase transformation beneath oxide scale and oxides is also detailed herein, contributing to further development and optimisation of HEA for high temperature applications.

High temperature oxidation regime transitions in hafnium carbide

AbstractUnderstanding the oxidation behavior of hafnium carbide is crucial to its application in extreme environments. In this work, the transition in high‐temperature oxidation kinetics regimes in hafnium carbide is explained based on phase equilibria considerations supported by observed changes in oxide scale microstructure evolution associated with different transformation pathways. Below, a composition‐dependent critical temperature and oxygen pressure, hafnium carbide first transforms to an amorphous material with nominal composition HfO2C followed by phase separation into carbon and hafnia domains. Subsequently, gaseous transport through a nanometric pore network formed by oxidative removal of phase‐separated carbon becomes rate‐limiting. Above this critical point, the oxidation sequence involves a direct transformation from hafnium carbide to hafnia and gaseous products, leading to dissimilar scale morphologies responsible for the reported transition from gaseous to solid‐state diffusion‐limited oxidation regimes at ultra‐high temperatures.

The effect of TiSi2 healing improver in self-healing ability of ceramics

A method to enhance the temperature range in which continuous self-healing fiber-reinforced ceramics (shFRCs) can self-heal is proposed to obtain a new high-temperature structural material. The effect of TiSi2 oxidation on self-healing was investigated using SiC, a typical self-healing agent, and TiSi2, which oxidizes at a lower temperature than SiC. Mixtures of SiC and TiSi2 powders were prepared by wet-mixing, and changes in their high-temperature oxidation behavior were investigated using thermogravimetry/differential thermal analysis. The oxidation of TiSi2 at 1000 °C enhanced the oxidation rate of SiC by 2–3 times. A shFRC consisting of an Al2O3 matrix, an interface layer of SiC and TiSi2, and Al2O3 fiber bundles was fabricated by slurrying and filament-winding. The strength recovery of the shFRC following three-point bending was investigated, and results indicated that the prepared material recovered 50 times faster than conventional shFRCs at 1000 °C. The self-healing improver described in this study can promote the oxidation of self-healing agents via its reaction heat. Thus, this improver may be applied as a practical component of self-healing materials.

Phase formation, structure and properties of quaternary MAX phase thin films in the Cr-V-C-Al system: A combinatorial study

Tailoring of individual atomic layers via alloying to synthesize quaternary MAX phases allows for expanding their chemical diversity and fine-tuning of their properties. In this study, Cr-V/C/Al multilayered precursors were deposited via combinatorial magnetron sputtering, creating nanostructured architectures with periodic stacking of nanolayers and varying Cr:V ratios. Their phase transformation and underlying reaction mechanisms during subsequent thermal annealing in argon towards the prospective quaternary solid solution (CrV)n+1AlCn MAX phases formation was systematically studied. Crystallization of (CrV)2AlC starts at approximately 500°C, while growth of higher-ordered (CrV)4AlC3 is observed from 960°C. Notably, intergrowth of (CrV)2AlC and (CrV)4AlC3 structures with coherent interface suggests that (CrV)2AlC acts as template for nucleation of (CrV)4AlC3. Thermal stability and high-temperature oxidation tests found that (CrV)2AlC exhibits higher thermal stability compared to (CrV)4AlC3 and films with Cr72.7V27.3 displayed good oxidation resistance at 1000°C, forming a protective bilayer oxide scale consisting of (Cr,Al)2O3 and Al2O3.

High-temperature oxidation and gas thermal shock studies of IC10 simulated specimens with thermal barrier coatings

PurposeThe purpose of this study is to investigate the effects of high-temperature oxidation tests and gas thermal shock tests on IC10 simulated components with thermal barrier coatings under different temperatures and oxidation times.Design/methodology/approachIn the high-temperature oxidation test, specimens were oxidized at three different temperatures of 850, 980, and 1,100 °C for durations of 10, 20, 50, 100, 200, and 300 h, respectively. In the gas thermal shock test, specimens were pre-oxidized for 10, 20, 50, and 100 h, followed by a high-temperature gas thermal shock test at 1,100 °C.FindingsIn the high-temperature oxidation tests, with increasing oxidation time, the oxidation layer thickened, and the air-film holes diameter decreased. The microstructure of the bond coat transitioned from strip-like to block-like, and internal cracks transformed from numerous and short to larger and deeper. Below the bond coat, a noticeable disappearance layer of strengthening phase appeared, with increasing thickness. The strengthening phase in the substrate transitioned from regular square shapes to circles as temperature increased. In gas thermal shock tests at 1,100 °C, the oxidation weight gain ratio increased with longer pre-oxidation times, whereas the erosion weight loss ratio gradually decreased.Originality/valueThe originality and significance of this study lie in its departure from the typical subjects of high-temperature oxidation and thermal shock tests. Unlike common research targets, this study focuses on IC10 simulative specimens with thermal barrier coatings and air-film holes. Furthermore, it investigates the effects of varying temperatures and oxidation durations.

Microscopic insights into the ammonia-methanol blended combustion at high temperatures

Ammonia and methanol have a broad application prospect in the future as green renewable liquid fuels. Methanol has high reactivity and good solubility with ammonia, which is conducive to solving the dilemma of ammonia combustion. However, there are few studies on ammonia-methanol blended combustion, and the effect of blended combustion on the reaction pathways needs to be further investigated. Therefore, this study used the reaction molecular dynamics simulations to reveal the role of methanol on the ammonia combustion and emission process at the microscopic level, focusing on the effects of different fuel blending ratios and oxygen concentration in the air under stoichiometric conditions. The variation of oxidation pathways from ammonia to NO and methanol to CO under different conditions was analyzed in detail. It was found that the methanol accelerated ammonia combustion mainly through enhancing OH production, but methanol and its intermediates inhibited the initial oxidation of ammonia. When the fuel blending ratio was 0.75, the system had lower fuel-type NO production alongside a higher ammonia consumption rate under stoichiometric conditions. The crucial role of NH in the HNO formation at high-temperature ammonia oxidation conditions was revealed. The pathway of HNO + OH → NO + H2O dominated the conversion of HNO to NO in this study. Increasing the methanol content promoted the conversion of NH to HNO and the pyrolysis of HNO while inhibiting the reaction between HNO and O2. In addition, the finding indicated that the high O2 level in air can enhance the reactions between ammonia and OH radicals but inhibit the pyrolysis of CH2OH/CH3O significantly.

Simultaneous improving high temperature oxidation resistance and room temperature toughness of Nb[sbnd]Si based alloy via appropriate Ta content addition strategy

NbSi based alloys are expected to become the application materials for high pressure turbine blades of aircraft engines. This paper investigates the impact of Ta addition on room temperature fracture toughness and isothermal oxidation behavior at 1250 °C of four NbSi based alloys with compositions of Nb-16Si-20Ti-8Zr-4Hf-1.5Al-xTa (x = 0, 1, 2, and 4 at.%) fabricated through vacuum non-consumable arc-melting. The results show that the room temperature fracture toughness and 1250 °C oxidation resistance of the alloys increase first and then decrease with the addition of Ta element. The room temperature fracture toughness of 1Ta alloy is the best, reaching 17.1 MPa·m1/2. Adding a moderate amount of Ta (1 at.%) significantly enhances the alloy's oxidation resistance, but an excessive Ta content diminishes this enhancement. This research has obtained a Nb-16Si-20Ti-8Zr-4Hf-1.5Al-1Ta alloy with high room temperature fracture toughness and excellent high temperature oxidation resistance simultaneously, which provide an ideal path for designing NbSi alloys with superior comprehensive properties.

Kinetics and mechanisms of high-temperature oxidation in BCC and FCC high-alloy Fe-based alloys with high volume fraction of carbides

This study conducts a detailed analysis of high-temperature oxidation and microstructural evolution in two high-alloy Fe-based alloys, each characterized by a high-volume fraction of carbides but differentiated by their matrices − body-centered cubic (BCC) and face-centered cubic (FCC), which was achieved by the addition of nickel. By investigating the intricate interplay of factors such as phase composition, nickel content, and the presence of carbides, this research aims to elucidate the diverse oxidation kinetics and underlying mechanisms specific to each alloy type. Results show that the BCC alloy exhibits slower oxidation kinetics compared to its FCC counterpart, suggesting better performance in high-temperature environments. Moreover, while both alloys develop strong adhesive oxide scales primarily composed of Cr2O3, the FCC alloy experiences more pronounced scale spallation and cracking. A faster progression of decarburization was observed in the BCC alloy. This comprehensive comparison highlights how variations in matrix structure, along with nickel content and carbide behavior, critically influence oxidation kinetics, scale adhesion, and the overall integrity of oxide scales. Understanding these nuanced interactions is crucial for designing high-performance alloys tailored for extreme operating conditions.

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

Tailoring oxidation resistance of Cantor alloy by addition of Ta and Al

High-entropy alloys are widely investigated for applications in the nuclear engineering field, the aerospace sector, and various other high-temperature applications. High-temperature oxidation behaviour is a typical issue in such applications. In the current work, an effort is made to tailor the oxidation behaviour of Cantor alloy (CoCrFeMnNi) in the air at 1000 °C with the addition of Ta and Al. Both CoCrFeMnNiTa as well as CoCrFeMnNiAl alloys exhibit considerable resistance to oxide scale spallation as well as develop multi-layered complex oxide scales. CoCrFeMnNiTa primarily forms rutile-type CrTaO4 oxide, which drastically reduces the inward diffusion of oxygen and nitrogen and suppresses the escape of other alloying elements. Nonetheless, the better result is obtained through the Al addition, as evidenced by the comparatively lower oxidation rate constant of CoCrFeMnNiAl in comparison to CoCrFeMnNiTa alloy. This is attributed to the superior oxidation resistance for CoCrFeMnNiAl could be related to the emergence of distinctive Cr2O3 and Al2O3 scales. Additionally, the oxide scale of CoCrFeMnNiTa was not completely smooth and showed some spallation whereas the oxide scales of CoCrFeMnNiAl remained smooth, continuous, and had stronger oxide-substrate interface adhesion.

Effect of Ag on High-Temperature Oxidation Behavior of Mg–6.5Gd–5.6Y–0.1Nd–0.01Ce–0.4Zr Alloy

Effect of Ag on High-Temperature Oxidation Behavior of Mg–6.5Gd–5.6Y–0.1Nd–0.01Ce–0.4Zr Alloy

Corrosion and oxidation behaviors of CoAlTiWTa RHEA coating on Inconel 718 superalloy prepared by laser cladding

CoAlTiWTa refractory high-entropy alloy (RHEA) coating was prepared on Inconel 718 superalloy by pulsed laser cladding. Corrosion behavior in 3.5 wt% NaCl solution at room temperature and oxidation behavior at 600 ℃ of the coating were systematically investigated. The electrochemical performance, surface morphology, and corrosion and oxidation products were carefully characterized. The results show that the RHEA coating has a higher corrosion potential, smaller corrosion current, higher resistance value, and a more obvious passivation effect. Duplex-layer oxide film composed of an internal Al2O3-TiO2 layer and an external Co oxide layer is formed on the RHEA coating, improving high-temperature oxidation resistance.

Effect of Ca and Y microalloying on oxidation behavior of AZ31 at high temperature

The microstructure, oxidation behaviour and oxide film morphology of AZ31, AZ31–0.5Ca, AZ31–0.5Y and AZ31–0.5Ca-0.5Y alloys were investigated. The results demonstrate that the oxidation behaviour of all the experimental alloys can be divided into two distinct parts: the incubation zone, which follows a parabolic law, and the non-protective oxidation zone. The resistance to high-temperature oxidation of AZ31 was enhanced by the incorporation of Ca or Y. The outcomes demonstrated that the oxidation behaviour of AZ31 was highly commendable. The observation of the micro-morphology by scanning electron microscopy (SEM) revealed that the presence of calcium (Ca) and yttrium (Y) can reduce the amount and change the shape of the low-melting-point phase of magnesium (Mg) and aluminium (Al) (Mg17Al12). The morphology and composition of the oxide films were analysed, and it was found that the AZ31–0.5Ca and AZ31–0.5Ca-0.5Y oxides are thinner and more dense, and that the failure is in the form of peeling and detachment. Furthermore, it was observed that the oxides of AZ31 and AZ31–0.5Y become loose and porous at high temperatures. The antioxidant capacity of calcium is enhanced by increasing the film density, while yttrium enhances the resistance to high-temperature oxidation by depleting the low-melting phase and changing the nature of α-Mg. The simultaneous addition of Ca and Y results in cracking and peeling of the film layer.

Effect of Ta on the high temperature oxidation behavior of Mo-based bulk metallic glasses

Mo-based bulk metallic glasses (BMGs) exhibited very high thermal stability and showed promising applications in high-temperature fields. However, their high-temperature oxidation resistance remains unsatisfactory. In this work, the effect of Ta (0–6 at.%) on the high-temperature oxidation behavior of MoCoB BMG was systematically investigated. The oxidation kinetics of MoCoB BMG and Ta-bearing Mo-based BMGs generally followed a parabolic law at 873–973 K, and the rate constants increased with the increasing temperature. The oxidation products of MoCoB BMG were primarily composed of CoMoO4 and MoO3, and the oxides of Ta-bearing Mo-based BMG were mainly CoMoO4, MoO3, CoTa2O6, and Ta2O5. The addition of Ta can significantly promote adhesion between the substrate and the external oxide layer, forming a dense spinel layer with a diffusion barrier that provides good oxidation resistance to the Mo-based BMG. The thin oxidation layer of Mo44Co34Ta6B16 was only about 13 μm after oxidation at 973 K for 120 h.

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.

Effect of continuous gradient Al on high-temperature oxidation of Ni-Cr-Co based superalloys via a high-throughput method

This study focuses on the effect of the main antioxidation element Al on the high-temperature oxidation resistance of Ni-Cr-Co based superalloys. A novel “3D printing-high temperature diffusion” high-throughput method was used to accurately determine the critical Al content to form continuous Al2O3 film. Results show that Al2O3 film significantly affects the element diffusion process during oxidation, and the critical Al content to form continuous Al2O3 film is 0.8 wt%. This conclusion was further confirmed by the corresponding discrete samples. It was also found that Ni-Cr-Co based superalloys exhibit “oxidation weight loss” and “Kp-antioxidation positive correlation” phenomena in high humidity condition.

Impact of Nb and Zr on the precipitation evolution of Laves phase and the properties of laser cladding coating of AlCoCrFeNi high entropy alloy

The impact of Nb, Zr, and their synergies on the phase composition, wear and high oxidation resistance of a high entropy laser cladding coating consisting of AlCoCrFeNi on Q235 steel was thoroughly investigated in this work. From our analysis, it was demonstrated that the addition of Nb and Zr promoted the formation of the Laves phase except the BCC phase, and a small amount of MC phase was formed in the coatings containing Zr. Although both of them can refine the grain to different degrees, the grain refinement degree was the highest when they were added together. The solid solution strengthening, fine crystal strengthening, and Laves phase precipitation strengthening induced by the addition of Nb and Zr can significantly improve the microhardness of the coating, which was 1.1–1.5 times that of S1-S3 coatings. The formation of ternary Laves phase, grain refinement, and increase of the microhardness enhanced the plastic deformation and micro-cutting resistance of S4 coating, and the wear resistance was 1.3–2.5 times that of S1-S3 coatings. The unstable oxide Nb2O5 produced by the addition of Nb led to a reduction in the stability of the oxide layer. However, when the two were added cooperatively, the formation of unstable oxide Nb2O5 was reduced by the presence of Zr. Moreover, grain refinement was induced by the collaboration of the two making the protective oxide layer form faster, and stronger bonding with the coating, the high temperature oxidation resistance was significantly improved, which was 1.3–4.3 times that of S1-S3 coatings.