Excellent High Temperature Oxidation Resistance Research Articles

Enhancing the high-temperature oxidation performance of AlCrTiSiN coating by in-situ generation of multi-layer antioxidant composite structures

A novel AlCrTiSiN high-entropy coating with superior thermal stability and high-temperature oxidation resistance, has been produced. The coating is characterized by unique fcc single-phase solid solution structure with uniform composition, severe lattice distortion and low fcc-AlN solubility, which results in the superior thermal stability. The excellent high-temperature oxidation resistance of coating is attributed to the multi-layer composite structures generated by in-situ reaction of element selective diffusion during the oxidation process. The inner dense SiO2-typed amorphous sub-layer and the intermediate (Al,Cr)2O3-typed sub-layer effectively block the O inward diffusion, and thus enhance the high-temperature oxidation resistance of the coating.

Fabrication of mechanically alloyed high entropy alloys (20-Fe-20Cr-20Ni-20Mn-20Ti) modified carbon paste electrode sensor for the cyclic voltammetric determination of methyl orange

We have successfully fabricated high entropy alloys (HEA) of composition 20-Fe-20Cr-20Ni-20Mn-20Ti by ball milling method for 20 h after optimizing the milling parameters. Generally, the HEAs are very popular for their multi-elemental cocktail effect and exhibit excellent high temperature oxidation resistance, high strength, electromagnetic, wear and corrosion resistance properties. But, HEAs also exhibit significant electrocatalytic properties due to their unique morphology, composition, and structure. Therefore, we have used planetary ball milled HEA powders for the electrochemical determination of methyl orange (MO). MO is recalcitrant and very difficult to degrade and can affect the humans as well as the environment. Therefore, we must determine the presence of MO. We have investigated the effect of scan rate, modifier and analyte concentration, and the pH variation on the anodic peak current (Ipa) of MO. The calculated active syrface area of bare carbon paste electrode (BCPE) and HEA-modified carbon paste electrode (HEA-MCPE) were found to be 0.041 cm2 and 0.137 cm2 respectively. We have obtained the maximum oxidation peak current for the 8 mg HEA-MCPE at a pH of 7.2 during the electrochemical oxidation of MO. The increased Ipa in basic medium is due to structural transformation of MO from quinoid form (in acidic medium) to azo structure (in basic medium). We have also calculated the number of electrons and the protons involved in the electrochemical reaction. The calculated values of detection limit (DL) and quantification limit (QL) of 8 mg HEA-MCPE was found to be 0.114 × 10−8 M and 0.38 × 10−8 M respectively.

Microstructure development of plasma sprayed dual-phase high entropy ceramic coating derived from spray dried and induction plasma spheroidized powder

Dual phase high entropy ceramics (DPHECs) exhibit excellent high temperature mechanical properties and oxidation resistance. Nevertheless, they cannot be applied in the structural components on large scale due to their intrinsic brittleness. Hence, DPHEC coating is a necessary development direction for industrial applications. In this study, we first fabricated micron-order DPHEC powder with high quality by precursor synthesis, spray drying (SD), and induction plasma spheroidization (IPS). The DPHEC coating was prepared by supersonic atmospheric plasma spraying (SAPS). The microstructure, phase compositions, and mechanical properties of the DPHEC powder and coating are investigated in detail. Results show that the SD&IPS powder and SAPS coating are all composed of HEB and HEC phases, showing slight composition segregation and typical global eutectic microstructure. The nanohardness and Young's modulus are 22.17 ± 2.76 GPa and 309.79 ± 35.71 GPa, respectively. The fracture toughness was calculated to be 2.23 ± 0.17 MPa m1/2 from the energy analysis method. The mechanical properties are enhanced by the solid solution and fine grain strengthening effects and are weakened by the intrinsic defects of plasma sprayed coating. This work provides a new method and a potential material for thermal spraying ultra-high temperature ceramic coatings.

Fire-resistant and thermal insulation performance of SiC nanofiber batt fabricated from cotton fiber batt

The cotton fiber batt is one of the most commonly used thermal insulator in our lives at room temperature because of its flexible and porous structure. The SiC nanofibers have excellent mechanical, physical, and chemical properties such as high mechanical strength and modulus, low density, high-temperature resistance, which is a promising material for high temperature structural materials or thermal insulator. In this work, a flexible SiC nanofiber batt was fabricated from the cotton fiber batt by sol-gel carbothermal reduction reaction. The fluffy carbonized porous cotton batt was used as a template for the fabrication of sponge-liked SiC nanofiber batt composed of single crystalline β-SiC fibers. It exhibits good compressive flexibility, ultra-high porosity (a specific surface area was 30.90 m²/g), excellent high-temperature stability (ranging from −196 °C in liquid nitrogen to 1300 °C under the flame of butane blowtorch) and low thermal conductivity (0.02 W/(m·K) at room temperature). The SiC nanofiber batt, which has low density, excellent high-temperature resistance and oxidation resistance, is a promising material for high-temperature structural materials or thermal insulators under extreme conditions. The facile fabrication method of SiC nanofiber batt from common cotton batt provides a novel technique for economic industrial production of high temperature thermal insulation material.

Effect of non-metallic silicon content on the microstructure and corrosion behaviour of AlCoCrFeNi high-entropy alloys

AlCoCrFeNi high-entropy alloys (HEAs) have shown excellent mechanical properties and high-temperature oxidation resistance but poor corrosion resistance owing to the high contents of the aluminium passivation film. In this study, Si was added to these alloys with the aim of improving the composition and stability of the passivation films. The microstructure and corrosion behaviour of AlCoCrFeNiSix (molar ratio x = 0, 0.1, 0.2, 0.3, and 0.4) HEAs were investigated. Dendritic and spinodal decomposition regions were observed in all five alloys. In the dendritic region, the dendritic structures transitioned from a petal shape to a dendritic shape with increasing Si content. Phase separation occurred in the spinodal decomposition region, which predominantly consisted of ordered body-centred cubic (B2) and disordered body-centred cubic (A2) phases. The size of the A2 phase decreased, and the amount of the A2 phase increased with increasing Si content. An optimised Si content could enhance the stability of Al and Cr passivation films, whereas excessive Si imposed an adverse effect by forming a Cr passivation film. The corrosion resistance of AlCoCrFeNiSi0.2 HEAs was optimum with a passive current density of 3.2 μA/cm2, which was 0.2 times that of the obtained AlCoCrFeNi HEAs without Si. The type of corrosion changed from local corrosion of AlCoCrFeNiSix (x ≤ 0.3) HEAs to general corrosion of AlCoCrFeNiSi0.4 HEAs. The corrosion mechanisms of the AlCoCrFeNi HEAs with various Si contents were elucidated.

Effect of TiAlN diffusion barrier at MoSi2-SiO2 composite coating/Mo alloy interface

In order to reduce the interdiffusion at interface of the silicide coating/Mo alloy and improve the service life of the coatings. MoSi2-SiO2 composite coatings with TiAlN diffusion barrier were prepared on Mo alloy by magnetron sputtering and followed by hot press sintering in the present study. Oxidation and interdiffusion behaviors of the samples were investigated at 1200 °C in static air. The results show that MoSi2-SiO2 composite coatings have excellent high temperature oxidation resistance, and the inward diffusion of Si is greatly inhibited with the addition of TiAlN diffusion barrier. After oxidation at 1200 °C for 100 h, the mass change of the MoSi2-SiO2 composite coatings is only -0.059 mg/cm2 to -0.022 mg/cm2, the thickness of the interdiffusion zone is just only 3.4 μm that is one order of magnitude smaller than TiAlN-free coating. The TiAlN diffusion barrier can effectively inhibit the interdiffusion of elements between the MoSi2-SiO2 composite coatings and the Mo alloy substrates.

Microstructure and properties of CoCrFeNiAlxMo2-x high-entropy alloy coating by laser cladding

CoCrFeNiAlxMo2-x (x = 0, 0.5, 1, 1.5, and 2) high-entropy alloy coatings were applied to Q235 steel, and this study investigated the effect of x variations on microstructure evolution and properties. It was fount that as x increased, the crystal structure of the coatings transitioned from a face-centred cubic (FCC) + body-centred cubic (BCC) + σ + B2 phase to a BCC + σ + B2 phase, and eventually it become a BCC phase. Concurrently, the microhardness, wear resistance, corrosion resistance, and high-temperature oxidation resistance of the coatings initially increased and then decreased with the rise in x. The optimal values were achieved at x = 1. The enhancement in microhardness and wear resistance of high-entropy alloy (HEA) coatings was attributed to the change of phase type, dispersion strengthening and solid solution strengthening. Adding of the Al element generated a passivation film on the coatings’ surface, which mitigated galvanic corrosion. Furthermore, an appropriate amount of Mo increased the thickness and density of the passivation film, thereby improving its corrosion resistance. During early-stage high-temperature oxidation, the Al underwent element undergoes rapid oxidation, while Mo promoted the formation of Al2O3, leading to an excellent high-temperature oxidation resistance. Additionally, mathematical model equations were used to fit the results, adding insights into the effects of Al and Mo content changes (x value) on the wear resistance, corrosion resistance, and high-temperature oxidation resistance of the coatings.

Gamma prime formation in nickel-based superalloy IN738LC manufactured by laser powder bed fusion

Complex components for high-temperature gas turbine applications require materials that offer a combination of excellent high-temperature strength and oxidation resistance. Nickel-based superalloys with high gamma prime (γ´) volume fractions are particularly suited for these applications, especially combined with additive manufacturing for intricate geometries. Despite the complex thermal history that these materials experience during laser powder bed fusion (LPBF) processing, γ´formation is suppressed when manufacturing IN738LC, which has a medium equilibrium γ´content of about 40–50 vol%. This study follows γ´formation in LPBF IN738LC during subsequent annealing treatments at temperatures ranging from 745 °C to 865 °C, creating an experimentally determined TTT (temperature-time-transformation) diagram. This diagram is largely based on scanning electron microscopy (SEM) imaging supported by Vickers hardness measurements and scanning transmission electron microscopy (STEM) bright field imaging. Atom probe tomography (APT) of the as-built material indicated nm-sized regions depleted in Cr and enriched in Ni, Al, and Ti, but show no characteristic superlattice patterns in TEM diffraction. APT and TEM diffraction analysis of material annealed at 850 °C for 3 min confirmed the presence of the γ´phase but indicated that γ´had formed through spinodal decomposition instead of precipitation.

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.

Highly controllable additive manufacturing of heterostructured nickel-based composites

Owing to hetero-deformation induced (HDI) strengthening and HDI work hardening, heterostructured materials with both “hard” and “soft” features have been proven to achieve strength–ductility synergy. Laser-directed energy deposition (LDED) has shown tremendous potential in the fabrication of heterostructured materials, but faces challenges in accurately placing the required structures or materials at specific times and locations. This study developed a novel Ti2AlC (MAX phase)-modified Inconel 718 composite material (MAX/Inconel 718) with multiscale precipitation (γ’, carbides, Laves phase) characteristics during solidification, highly sensitive to changes in cooling rates, and exhibiting excellent controllability of strength. A method called multibeam diameter laser-directed energy deposition (MBD-LDED), which allows the dynamic adjustment of the beam diameter during the building process to alter the cooling rate during solidification, is proposed. This enabled the placement of MAX/Inconel 718 with different strengths at suitable positions within the part. Different combinations of beam diameters can form periodic distributions and spatial interlocking structures with alternating “soft” and “hard” features perpendicular and parallel to the building direction. Compared to commercial Inconel 718, MAX/Inconel 718 demonstrated excellent manufacturability, strength, and high-temperature oxidation resistance. This study provides new insights into the design and performance optimisation of heterostructures using homogeneous materials and offers guidance for the integrated manufacturing of heterostructured components in the context of comprehensive material–structure–performance design.

Stability of the ternary τ11-Al4Fe1.7Si intermetallic phase from experiment and Ab initio calculations

The Al-Fe-Si ternary system provides an opportunity for the design of new lightweight low cost alloys that have high melting temperature, superior strength, and excellent high-temperature corrosion and oxidation resistance. This system is exceptionally complex and exhibits up to 21 reported binary and ternary compounds. The intermetallic compound τ11-Al4Fe1.7Si is of particular interest due to its low theoretical density, promising mechanical properties, and low cost constituent elements. Knowledge of the exact composition range and thermal stability of this phase is crucial for further development. In this study, Al-Fe-Si alloys were fabricated and equilibrated at 800 and 950 °C. The composition range of τ11-Al4Fe1.7Si was analyzed using scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction to confirm the presence of the phase. Density functional theory calculations show that entropic contributions drive and stabilize the τ11-Al4Fe1.7Si phase. Based on experimental measurements, the composition range of τ11-Al4Fe1.7Si phase was determined to be Al-(24.3–25.5)Fe-(8.2–10.8)Si at% and Al-(24.6–25.2)Fe-(9.6–11.0)Si at% at 800 °C and 950 °C, respectively.

Tribological, oxidation and corrosion properties of ceramic coating on AISI H13 steel by rare earth-Cr composite boronizing

In this paper, a rare earth-Cr composite boronizing method to prepare boride ceramic coatings for AISI H13 steel was proposed. The effect of rare earth elements and Cr on the microstructure, hardness, wear resistance, high temperature oxidation resistance, and corrosion of boride ceramic layers was researched. The characteristics of the boride layers were investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), electron probe microanalysis (EPMA), wear tests, high-temperature oxidation tests, and corrosion immersion tests, etc. The results showed that the boride layer comprised of Fe2B, FeB, CrB and Cr2B phases. The addition of rare earth CeO2 and Cr nanopowder promoted the growth of the boride layer, and its surface hardness increased by 3.5 times compared with that of tempered AISI H13 steel. In addition, the addition of CeO2 and Cr significantly reduced the wear rate of the boride layer, with the surface wear mechanism being abrasive oxidative wear. Furthermore, the oxidation rate of the boride layer was 71 % lower than that of AISI H13 steel, demonstrating excellent high-temperature oxidation resistance; and the boride layer showed good acid corrosion resistance in corrosion immersion tests.

Electrochemical silicification of Mo in molten CaCl2–CaSiO3 enhances high-temperature oxidation resistance

This work aims to demonstrate the feasibility and effectiveness of electrochemical silicification of Mo in molten CaCl2–CaSiO3. Through constant-current electrolysis at 1123 K, high-quality α-MoSi2 coatings are successfully deposited on Mo plates, following the sequential formation of Mo5Si3 and β-MoSi2 phases. Increased current density results in grain refinement and reduced surface roughness due to the increase in overpotential. The oxidation test indicates that the silicide-coated Mo plate can withstand exposure to air at 1573 K for more than 15 h with minimal damage, showcasing the excellent high-temperature oxidation resistance. These findings highlight the potential application of the electrochemical silicification process.

Solid Oxide Membrane-assisted Controllable Electrolytic Fabrication of Ti5Si3/TiC Composites in Molten Salt

Background: The titanium silicide Ti5Si3 possesses many desirable properties, such as a high melting point, excellent high-temperature oxidation resistance, low density, and relatively high hardness, and it is considered a promising structural intermetallic compound. However, like most ceramic materials, originating from low symmetry (D88) in its crystal structure, Ti5Si3 has poor fracture toughness and limited flexibility at room temperature, and at high temperatures, its creep resistance also drops sharply, which hinders its application. To overcome these shortcomings, it is suggested that TiC is a practical addition to Ti5Si3 to overcome the brittleness. Compared with monolithic Ti5Si3, Ti5Si3/TiC composites have a higher fracture toughness. Ti5Si3/TiC composites can be prepared by many ways, which commonly require high energy cost, complex processes and provide low efficiency. Therefore, the search for environmentally friendly strategies for the production of Ti5Si3/TiC is still ongoing. Objective: This article proves that we can successfully prepare Ti5Si3/TiC composites from CaTiO3/SiO2/C precursor by using SOM technology and explores the reaction mechanism of electrochemical process. Methods: In the process of electroreduction of CaTiO3/SiO2/C particles into Ti5Si3/TiC composites, we mainly used SOM technology at 1273 K and 4.0 V in molten CaCl2 and under an argon atmosphere. Results: The results show that the Ti5Si3/TiC composites can also be successfully electrosynthesized from CaTiO3/SiO2/C precursors by using SOM-based anode systems at 1273 K and 4.0 V in molten CaCl2. Conclusion: This work demonstrates that Ti5Si3/TiC composites have been successfully electrosynthesized from CaTiO3/SiO2/C precursors using SOM-based anode systems at 1273 K and 4.0 V in molten CaCl2. The Ti5Si3/TiC has a smooth surface and micro/nano-porous structure. The formation routes for Ti5Si3 and TiC are independent. In summary, the SOM-assisted controllable electroreduction process has the potential to provide a novel one-step route from CaTiO3/ SiO2/C precursors to Ti5Si3/TiC composites in molten salts.

New insights in the oxidation behavior of (FeCoCrNi)94Al4Ti2Six high entropy alloys at 1100 °C

A new high-entropy alloy (FeCoNiCr)94Al4Ti2Six with excellent high-temperature oxidation resistance at 1100°C has been developed. The inner oxide behavior with Si added is the key factor of its oxidation resistance. The effect of Si content on the types, continuity, spalling resistance, and diffusion inhibition property of the inner oxide layer were revealed. An internal nitridation of Ti phenomenon was observed in this HEA and the preferential formation of TiN was confirmed by DFT calculation. A novel model for the oxidation resistance of high-entropy alloys affected by silicon is proposed.

Effect of yttrium on the formation, microstructure and high-temperature oxidation resistance of the oxide film on the surface of FeCr alloy

Yttrium was diffused into the surface layer of FeCr alloy using an electrodeposition–thermal method via yttrium nitrate solution and diffusion annealing at 1000 °C. Y-doped FeCr samples exhibited excellent high-temperature oxidation resistance. The mass gains and spallation of Y-doped FeCr samples were only 0.51–0.64 mg/cm2 and 0.19–0.25 mg/cm2, respectively, and much lower than the alloy without yttrium (20.7 mg/cm2 and 9.08 mg/cm2, respectively) when oxidized in air at 900 °C for 200 h. The presence of yttrium increased the number of oxide nucleation sites, led to the transformation of the oxide from the Cr2O3 phase to the spinel (FeCrY)3O4 phase and accelerated the rapid formation of a continuous oxide film in the initial oxidation stage. The yttrium content affected the formation and microstructure of oxide film due to the lattice distortion of the FeCr phase. Excess Y induced formation of Y2O3 at grain boundaries, which further increased the bonding force between the oxide film and the substrate. A first-principles calculation confirmed that the bond strength between Y and other atoms was improved significantly. The length of the CrY bond showed little change under an external stress, which increased the bonding strength of the FeCr/Cr2O3 interface.

High temperature oxidation behavior of NiCoCrAlFeY high entropy bond coating fabricated by high-speed laser cladding

The low-diluted NiCoCrAlFeY high entropy bond coating is prepared by high-speed laser cladding (HSLC). Investigation shows it exhibits excellent high temperature oxidation resistance and slow TGO (thermally growth oxides) growth rate, for a protective α-Al2O3 layer fast covering its surface. Meanwhile, the bulk-like structure by HSLC process suppress the internal oxidation effectively. The severe lattice distortion of high entropy composition makes high diffusion energy and low diffusion coefficient for Al, leading the Al slowly consumed in the coating. Results confirm the bond coating deposited by HSLC possess a tremendous potential application at elevated temperature.

Oxidation mechanisms of a Cr[sbnd]Si alloyed coating-free press-hardened steel under simulated press hardening conditions

Press-hardened steel (PHS) undergoes severe high-temperature oxidation after press hardening, which significantly degrades surface quality and increases manufacturing cost. This work reports the mechanism by which a coating-free PHS (CF-PHS) with the simultaneous presence of Cr, Si, and Mn alloying elements achieves excellent high-temperature oxidation resistance. It is found that Si and Mn in the CF-PHS promote the formation of a continuous Cr2O3 layer with good protective effect, thereby improving high-temperature oxidation resistance, during the press hardening. Moreover, the continuous amorphous SiO2 layer formed at the oxide scale/matrix interface and the Mn-rich oxides that improve the compactness of the scale further enhance the oxidation resistance of the CF-PHS.

Mechanisms of Al2O3 and Cr2O3 formation during FeCrAl alloy Oxidation: A First-Principles study

FeCrAl alloys are the best candidates for nuclear fuel cladding materials due to their excellent corrosion resistance and high-temperature oxidation resistance. However, the oxidation mechanisms of them have not been fully explained. In this study, we investigate the oxygen adsorption on the surface of FeCrAl alloys using density functional theory. Our results reveal that Cr are prone to interact with O. Furthermore, an increasing number of Cr atoms in the adsorption configuration leads to a higher absolute value of the adsorption energy, especially for three Cr (-4.48 eV). To gain further insights, we conduct an analysis of their charge and orbital interactions. We find that Al atoms transfer the most charge to O atoms, resulting in the most stable bonding. This finding explains the experimental phenomenon where Cr2O3 is primarily observed at low temperatures or in the initial oxidation stage, while Al2O3 is observed at high temperatures during prolonged oxidation. This study highlights the variations in the behavior of metal atoms during their interaction with oxygen at atomic level. These findings contribute to the understanding of FeCrAl alloys’ exceptional oxidation resistance. Moreover, this research serves as a valuable scholarly reference for the advancement of FeCrAl alloys for their oxidization resistance.

Single-source-precursor synthesis of dense monolithic SiC/(Ti0.25Zr0.25Hf0.25Ta0.25)C ceramic nanocomposite with excellent high-temperature oxidation resistance

A dense monolithic SiC/(Ti0.25Zr0.25Hf0.25Ta0.25)C ceramic nanocomposite containing high-entropy carbide phase was prepared using a single-source-precursor method combined with spark plasma sintering. The nanocomposites were characterized by a unique microstructure with a homogeneous dispersion of (Ti0.25Zr0.25Hf0.25Ta0.25)C@C core-shell nanoparticles within a β-SiC matrix. The atomic ratios of transition metal elements within the in situ generated (Ti0.25Zr0.25Hf0.25Ta0.25)C nanoparticles can be controlled precisely by molecular design of the preceramic precursors. Oxidation behavior of the SiC/(Ti0.25Zr0.25Hf0.25Ta0.25)C nanocomposite was investigated as well. The SiC/(Ti0.25Zr0.25Hf0.25Ta0.25)C exhibit excellent oxidation resistance between 1200 °C and 1500 °C due to the in situ generated continuous multiphase scales consisting of β-SiO2, HfTiO4, ZrSiO4, HfSiO4, and Ta2O5 that can be rapidly sintered during oxidation. Particularly, at 1200 °C, the parabolic oxidation rate constant (Kp) value is 1–2 orders of magnitude lower than that of similar SiC/HfC, SiC/(Hf, Ta)C, SiC/(Hf, Ti)C and SiC/(Hf, Zr, Ti)C nanocomposites.