Improved Oxidation Resistance Research Articles

Initial Multidisciplinary Study of Oxidized Chromium-Coated Zirconium Alloy for Fuel Cladding of SCW-SMR Concept: Weight-Gain and Thermal Conductivity Measurements and Coating Cost Evaluation

One of the challenges of small modular reactors (SMRs) in comparison with large reactors is the greater difficulty in achieving high burnups in smaller cores. With greater neutron leakage through the periphery, a key factor is the neutron economy of the fuel cladding. However, all large supercritical water-cooled reactor (SCWR) concepts have employed neutron-absorbing stainless steels and nickel-based alloys in order to meet all the requirements in terms of corrosion and thermalhydraulics. In order to achieve higher burnups and extend the time between refueling in a SCW-SMR, the use of chromium-coated zirconium alloy as a potential fuel cladding candidate has been explored. Chromium coatings up to a few micrometers thick have shown improved oxidation resistance of zirconium-based claddings under operating conditions relevant to SCWR concepts. In this study, Zr-2.5Nb alloy (UNS R60904) from pressure tube samples was coated using a physical vapor-deposition (PVD) method. Oxidation tests were performed on coated samples at 500 °C and approximately 25 MPa in a refreshed autoclave. The effects of the oxide on heat transfer and hydraulic resistance are also discussed in this study. Last, but not least, this study evaluates the coating cost of the fuel cladding with chromium in a vacuum plasma spray process.

Atomistic simulation on the nano-scale oxidation of Fe-Cr alloy surfaces and the diffusion behavior of oxygen

The oxidation of Fe-Cr alloy surfaces was performed by reactive molecular dynamics (MD) simulations. The results shown that the addition of Cr caused a slow internal diffusion of oxygen with a thinner oxide layer in the Fe-Cr alloy, indicating improved oxidation resistance. Furthermore, the achievement of the saturation point in the diffusion flux of oxygen in Fe-Cr alloy was closely linked to the oxide structure, the formation of FeO may inhibit further oxidation by preventing more oxygen ions from reaching the unoxidized interior. Therefore, the evolution of oxide structure played a crucial role in improving the oxidation resistance of Fe-Cr alloys.

Pyrrole/MXene membranes with simultaneously high structural stability and permeability for nanofiltration: Implication for water transport

Laminar MXene membranes hold great promise for aqueous separation applications. However, their susceptibility to oxidation in water cause chemical degradation and functional loss, impeding their separation efficiency and durability. In this study, an enhanced MXene nanofiltration membrane was fabricated by simply incorporating pyrrole with Ti3C2Tx, resulting in significantly improved oxidation resistance and permeability. Compared with pure MXene membrane, the pyrrole/MXene membrane exhibited a 3.52-fold increase in water permeance (465.9 L m−2 h−1 bar−1) and achieved excellent rejection performance for various dye molecules. The molecular dynamics simulations revealed that the pyrrole/MXene system presented a higher diffusion coefficient due to the weaker interaction energy at the interface between water molecule and pyrrole/MXene membrane. Normally, a larger transmembrane energy barrier meant a higher transport resistance that prevented the molecule from passing through the membrane. In this way, the determination of activation energy showed that the introduction of pyrrole facilitated a reduction in the requisite activation energy of water transfer from 9.37 to 4.86 kJ mol−1. More importantly, we explored the fact that the stabilization of MXene membranes had a significant impact on their separation performance during a long-term operation. Compared with pristine MXene membrane, the pyrrole/MXene membrane maintained initial two-dimensional structure and stable nanofiltration performance after prolonged operation. The radial distribution function calculations demonstrated that the chemical interactions between Ti3C2Tx and pyrrole were strong and involved the formation of Ti–C bonding and intermolecular interaction. This research provides a facile and effective method to prepare a high-performance and stable MXene nanofiltration membrane.

Study on the electrical properties of Cu-based ECMs prepared by TiBN powder instead of W

In this work, TiBN and W were used as reinforced phases for Cu-based electrical contact materials. The microstructure, resistivity and arc corrosion resistance of Cu/TiBN and Cu/W alloys were investigated to understand the effect of TiBN and W doping on Cu/TiBN and Cu/W electrical contacts, respectively. Significant improvement in electrical conductivity, oxidation resistance and arc corrosion resistance of copper-based alloy was observed by TiBN reinforcement. Cu/TiBN composites showed good corrosion resistance to arc corrosion under atmospheric and salt spray conditions. The results showed the presence of large amount of TixOy, B2O3, N2 and other substances in Cu/TiBN system which are responsible for the improvement of arc corrosion resistance of Cu/TiBN system. The new Cu/TiBN electrical contact material showed great potential due to its excellent mechanical properties and arc corrosion resistance.

Improved oxidation resistance of Cr/FeCrAl coating on Zr alloy in high-temperature steam environment

A new bi-layer Cr/FeCrAl coating was successfully fabricated on the Zr-4 plates through multi-arc ion plating in order to take advantage of the two materials of FeCrAl and Cr. The high-temperature steam oxidation behavior of the Cr/FeCrAl-coated Zr-4 at 1000–1200 °C was investigated and compared with that of bare and single-layer FeCrAl-coated Zr-4. Various analytical techniques including scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for the microstructural and compositional analysis of the as-deposited and oxidized samples. Results indicated that the FeCrAl-coated Zr-4 could only withstand up to 1000 °C because of the severe FeZr interdiffusion. Whereas the introduction of the Cr interlayer effectively prevented fast FeZr interdiffusion and consequently improves the overall oxidation resistance of the Zr substrate below 1200 °C steam environment. After 1100 °C steam oxidation, the weight gain of the Cr/FeCrAl-coated Zr-4 was about 8 times and 2 times lower than that of the uncoated and FeCrAl-coated Zr-4 alloys, respectively. These facts make possible the use of FeCrAl coating on Zr cladding which has excellent high-temperature mechanical properties and oxidation resistance.

Effect of CrMoN addition on the thermal stability and cyclic impact resistance of TiVN coatings

By adding V atoms to TiN, the tribological and mechanical properties of TiVN coatings are improved. Multilayered coatings, rather than monolayered ones, may further enhance the mechanical properties and thermal stabilities of TiVN. Therefore, an approach was employed in this study to synthesize gradient-and-multilayered CrMoN/TiVN coatings through vacuum arc ion plating. During the impact fatigue test that utilized a cyclic loading device, the correlation between cyclic impact resistance and coating structures of the deposited coatings were evaluated. Vacuum annealing and high temperature oxidation at temperatures exceeding 600 °C were used to assess the thermal stability of the coatings. Although the as-deposited TiVN coating achieved the highest hardness of 30.2 ± 2.5 GPa, the CrMoN/TiVN multilayer coating only experienced a slight decrease to 29.1 ± 2.2 GPa, which exceeded the solid solution quaternary CrMoTiVN mixture rule prediction. When compared to the high-hardness monolayered TiVN and the low-hardness CrMoN, the CrMoN/TiVN multilayer coatings demonstrated the best resistance to cyclic impact. The TiVN coating displayed the worst oxidation resistance, as shown by the emergence of elongated vanadium-rich Ti-V oxide slats on the surface after oxidation. The CrMoN coating exhibited higher oxidation resistance than TiVN, and small granular chromium oxides formed on the surface beyond 700 °C. The addition of CrMoN to TiVN to form CrMoN/TiVN resulted in improved oxidation resistance by inhibiting the oxidation of TiVN. A different oxidation behavior was found for the CrMoN/TiVN coatings. The design of gradient-and-multilayered CrMoN/TiVN coatings is proven to be advantageous for applications that aim to enhance the thermal stability and cyclic impact resistance of mechanical tools.

Correlation between crystallite size, resistance to oxidation, and phase transformation of germanium-doped Fe3O4 nanocrystalline thin films by using a sputtering target of α-Fe2O3

We investigated the correlation between the crystallite size, resistance to oxidation, and phase transition of Ge-doped Fe3O4 nanocrystalline thin films. We prepared thin films on water-cooled glass substrates by radiofrequency sputtering with Ge-tipped α-Fe2O3 ceramic disks as targets. The addition of Ge caused a reductive phase transition from α-Fe2O3 with a corundum structure to Ge-doped Fe3O4 with an inverse spinel structure, resulting in a crystallite size of <10 nm. We annealed three samples with average sizes of 5, 8, and 10 nm by changing Ge addition concentrations at 673 K in air for up to 323 days until reaching near-thermal equilibrium. All samples maintained their magnetization at almost a constant value over long-term heat treatment. The results of Raman spectroscopy and optical transmittance spectroscopy suggest that there was a phase transition to Ge-doped γ-Fe2O3 at 5 nm, Ge-doped Fe3−δO4 with iron vacancies δ at 8 nm, and Ge-doped Fe3O4 at 10 nm. In other words, we retained Fe3O4 down to a relatively small crystallite size of 10 nm because of the improved oxidation resistance imparted by Ge doping.

La(Ca)CrO3-Filled SiCN Precursor Thin Film Temperature Sensor Capable to Measure up to 1100 °C High Temperature.

Thin-film sensors are regarded as advanced technologies for in situ condition monitoring of components operating in harsh environments, such as aerospace engines. Nevertheless, these sensors encounter challenges due to the high-temperature oxidation of materials and intricate manufacturing processes. This paper presents a simple method to fabricate high temperature-resistant oxidized SiCN precursor and La(Ca)CrO3 composite thin film temperature sensors by screen printing and air annealing. The developed sensor demonstrates a broad temperature response ranging from 200 °C to 1100 °C with negative temperature coefficients (NTC). It exhibits exceptional resistance to high-temperature oxidation and maintains performance stability. Notably, the sensor's resistance changes by 3% after exposure to an 1100 °C air environment for 1 h. This oxidation resistance improvement surpasses the currently reported SiCN precursor thin-film sensors. Additionally, the sensor's temperature coefficient of resistance (TCR) can reach up to -7900 ppm/°C at 200 °C. This strategy is expected to be used for other high-temperature thin-film sensors such as strain gauges, heat flux sensors, and thermocouples. There is great potential for applications in high-temperature field monitoring.

Effect of Al content on the microstructure, properties, and oxidation behaviors at 900 ℃ of (MoNbCoCrAlxSi0.2)70Ti30 refractory high-entropy alloys coatings fabricated by electron beam cladding

Electron beam cladding (MoNbCoCrAlxSi0.2)70Ti30 RHEAs coatings with different Al contents on the surface of Ti600 alloy, and their microstructure and properties were investigated. Two solid solution phases, A2/B2-BCC1 and A2-BCC2, and precipitated phases (Ti,Mo,Nb,Al)5Si3-IMC were found. The mechanical properties and wear resistance of RHEAs coatings increase and then decrease with increasing Al. The mechanism of the change in mechanical properties and wear resistance is based on the strong and weak relation between solid solution strengthening and precipitation strengthening. The improvement of high-temperature oxidation resistance is due to the promotion of Al2O3 formation at the early oxidation stage.

Improvement of oxidation resistance and alumina regrowth ability of Ni-30Cr-5Al alloy without and with Y: Nanocrystallization effect

Nanocrystallization of Ni-Cr-Al alloys decreases critical Al content (NAl*) for Al2O3 scale formation down to a level much lower than practical alloy Al content (NAl), and this is particularly prominent for the alloys with NAl≤ NAl*. In this work, oxidation of coarse-grained (CG) Ni-30Cr-5Al with NAl > NAl* and its nanocrystalline (NC) counterpart has been studied, with the focuses on the following issues: (i) nanocrystallization effect on Al2O3 steady-state growth and regrowth; (ii) nanograin growth effect on Al2O3 adhesion; and (iii) role of Y played in NC alloys by comparing the differences in oxidation of the NC alloys without and with Y.

A prediction of the thermodynamic, thermophysical, and mechanical properties of CrTaO4 from first principles

AbstractIt is reported that the self‐forming CrTaO4 oxide scale can protect refractory high‐entropy alloys from oxidation, superior to Cr2O3. In this paper, the phase stability, mechanical, and thermal properties of three polymorphous phases of CrTaO4 are systematically investigated from first‐principles density functional theory calculations. The mechanical properties predicted using the strain–energy methods indicated that all three phases are mechanically stable. The temperature dependence of elastic constants and polycrystalline moduli of three phases demonstrated the thermal softening as temperature increase. The Helmholtz‐free energies as a function of volume and temperature are derived from phonon dispersions within the quasi‐harmonic approximation at six strained volumes. The calculated apparent bulk coefficients of thermal expansion of these three phases are evaluated, the highest value approximately 13.4× 10−6 K−1 within a temperature range of 500–2000 K for the rutile I41md phase. The lattice thermal conductivity calculated by the Debye–Callaway model suggested that the rutile type I41md phase has the lowest value of approximately 2.1 W/m/K at 1800 K. The other two phases, C2/m and P2/c, exhibit higher values due to relatively lower Grüneisen parameters and larger phonon velocities. The melting point of CrTaO4 is predicted to be between 1975 and 2449 K using ab initio molecular dynamics simulations. This work provides a comprehensive theoretical understanding of the thermodynamic, mechanical, and thermal properties for the new material CrTaO4 and serves as an example of a viable computational design strategy for improved oxidation resistance of refractory alloys at high temperatures.

Initial oxidation mechanism of FeCrAl thin films with Nb and Si additions

FeCrAl thin films are considered optimal candidates for protecting surfaces in harsh environments, with potential for improvement in their anti-oxidation properties by incorporating beneficial dopants such as Nb and Si. However, the thermodynamic mechanism responsible for this improvement remains unknown. This study investigates the impact of Nb and Si additions on the growth mechanism of oxide formation during the initial stage of 1000°C air exposure. Spectroscopic analyses indicate the inception stage is characterized by the formation of α-Al2O3, accompanied by the generation of Cr-, Nb-, and Si-containing oxides. Thermodynamic calculations reveal that the additions of both Nb and Si can stabilize the phase structure of the thin films before oxide scale formation occurs, slowing down oxidation rates. Nb is shown to increase Cr activity, while Si enhances Al activity, promoting the formation of Cr-rich and Al-rich oxides respectively. This contributes to improvements in the thin films’ anti-oxidation properties. Overall, this research sheds light on the origin of the improved oxidation resistance of FeCrAl thin films containing Nb and Si.

Improving oxidation resistance of TaMoZrTiAl refractory high entropy alloys via Nb and Si alloying

Here, we investigate the interplay effects of Si and Nb alloying on the oxidation behaviors of the refractory high entropy alloys (RHEAs) at 1000 ℃. The alloying of Nb and Si promotes the formation of dendritic microstructures, suppresses the transition from parabolic to linear oxidation kinetics and significantly improves the oxidation resistance. Severe cracking of oxide scales is also reduced via Nb and Si alloying. According to the scanning transmission electron microscopy analysis, ZrO2 and TiO2 are initially formed during oxidation, and oxidation proceeds with the inward diffusion of oxygen, preferentially through the interdendritic region and BCC grain boundaries.

Improvement of oxidation resistance of arc furnace graphite electrodes

Improvement of oxidation resistance of arc furnace graphite electrodes

Microstructure evolution and cyclic oxidation performance of Cr2AlC transition layer as active diffusion barrier for Ni-based superalloy and NiCrAlY coating

Cr2AlC transition layer between the NiCrAlY coating and K417G superalloy was prepared to improve oxidation resistance of conventional NiCrAlY coating. Long-term cyclic oxidation was conducted at 1000 °C. Cr2AlC transition layer decomposed to Cr7C3 after annealing and further transformed to thermodynamically more stable continuous Cr23C6 during subsequent oxidation. Continuous Cr23C6 effectively blocked diffusion between NiCrAlY coating and substrate. Cr2AlC transition layer also supplied additional Al for NiCrAlY coating, greatly extended service life of the NiCrAlY coating. Furthermore, Cr2AlC, Cr23C6 and Cr7C3 were thermally matched to substrate and coating, avoiding coating spallation during cyclic oxidation.

Oxidation resistance improvement of carbon fiber nonwoven fabrics through SiC coating technology

The oxidation resistance of carbon fiber (CF) was enhanced by SiC coating layer. A hybrid sol–gel approach and chemical vapor reaction (CVR) were utilized to produce coating layer. SiO2 was applied to the CF surface, after which SiOx and SiH4 vapor were added via CVR method to intensify SiC formation and bonding. Interfacial bonding was further reinforced by the addition of graphene oxide (GO) prior to heat treatment. Three different samples were generated, and the gas liberated upon conversion to SiC was evaluated to determine relationships with microstructure. The amount of gas released differed depending on the chemical used in the sol–gel, and the mechanism of SiC formation under different conditions was also distinct. The results of a flame test indicated approximately 20% improvement in oxidation resistance compared to CF. The proposed SiC coating can circumvent the restricted process method that necessitates specialized equipment to manufacture high-quality CF with improved oxidation resistance.

Improved oxidation resistance of Cr-Si coated Zircaloy with an in-situ formed Zr2Si diffusion barrier

In the present study, the dense Cr and Cr0.92Si0.08 coatings have been deposited on Zircaloy-4 substrates by the magnetron sputtering technique. The high-temperature oxidation resistance of coatings is evaluated in 1200 °C steam for 1–4 h. The Cr0.92Si0.08 coating shows better oxidation resistance than the Cr coating. The in-situ formed Zr2Si diffusion barrier inhibits the mutual diffusion of Cr and Zr. And the formation of a Cr2O3/SiO2 double-layer scale effectively improves the oxidation resistance of a single Cr2O3 layer. The formation of the in-situ diffusion barrier, Cr2O3/SiO2 scales and oxidation protection mechanisms of the Cr0.92Si0.08 coating have been discussed in detail.

Investigating the Impact of Fly-Ash Additive on Viscosity Reduction at Different Temperatures: A Comparative Analysis

The viscosity of lubricating oils is influenced by fly-ash additives and temperature, as they play a crucial role in regulating the viscosity of oils. Fly-ash additives are added to lubricating oils to improve oxidation resistance and prevent deposit formation, which may reduce viscosity loss at high temperatures. This study aimed to investigate the impact of fly-ash additives and temperature on the viscosity of oils B, C, and A. The experimental methodology involved comparing the viscosity of these oils with and without the addition of a 0.5% fly-ash additive. Viscosity measurements were taken at different temperatures. The results showed significant changes in viscosity after incorporating the fly-ash additive. At 25 °C, oils B, C, and A exhibited viscosity increases of 6.2%, 8.1%, and 13.8%, respectively, compared to the samples without the additive. Similarly, at 75 °C, the viscosity increments were 10.2%, 11.5%, and 22.8% for oils B, C, and A, respectively. At 85 °C, the corresponding increments were 11.1%, 16.6%, and 32.8%. These findings highlight the effectiveness of fly-ash additives in reducing the impact of temperature on oil viscosity, with oil A demonstrating the highest efficacy. By adjusting the viscosity of the oil at different temperatures, the fly-ash additives contribute to maintaining stable lubricating performance. Understanding the influence of fly-ash additives and temperature on oil viscosity is crucial for optimizing the performance of lubricants across various temperature conditions. Additionally, this knowledge assists in selecting the appropriate additive ratios for specific applications, thereby ensuring optimal lubricant performance.

Oxidation behavior of high Cr white iron composites reinforced with TiC and nonstoichiometric TiCx in air at 600 °C

High Cr white irons (HCWIs) are often used as high-temperature components exposed to the temperatures exceeding 500 °C. Improving oxidation resistance of HCWI components is necessary for engineering applications. In the present study, oxidation behaviors of high Cr white iron (HCWI) and its composites reinforced with 1–2 μm nonstoichiometric TiCx resulting from the decomposition of Ti3AlC2 (in situ TiCx/HCWI), and 2–4 μm irregular-shape of TiC (TiC/HCWI) at 600 °C for 96 h in air were investigated. Results showed that the two composites exhibited better oxidation resistance than the pure HCWI material. The oxidation test revealed a weight loss for the unreinforced HCWI but a weight gain for the composites. Among these materials, the in situ TiCx/HCWI composite has the best oxidation resistance due to its dense and fine microstructure. Oxidative thermodynamics and oxidation mechanism were discussed. This work suggests that in situ formed TiCx is an effective reinforcement to improve the oxidation resistance of HCWIs.

Improvement of high-temperature oxidation resistance of WC–Co–Ni alloy by Cr3C2–CeO2–WS2 mixed additives and its mechanism

Whether used as hot rollers or hot forging dies, the high-temperature oxidation resistance of cemented carbides is closely related to their lifetime. In the context of the above applications, a WC–Co–Ni alloy with Cr3C2–CeO2–WS2 mixed additives is designed based on the principles of oxidation resistance and self-lubrication at elevated temperatures. The results of continuous oxidation at 700 °C for 16 h show that the oxidation rate of WC–6Co–6Ni–1.2Cr3C2–1.0CeO2–0.4WS2 (alloy 2#) with ultrafine dispersion phase Ce2O2S2 decreases by 23.7% and 15.4%, respectively, compared with WC–6Co–6Ni (alloy 1#) and WC–6Co–6Ni–1.2Cr3C2 (alloy 3#). The additives of Cr3C2 and CeO2 can promote the in situ atomic recombination in the binder phase and rapid nucleation of (Ni,Co,Cr)WO4. As a result, a 2.3 times and 1.6 times higher MWO4 (M = Co, Ni, Cr) in quantity is formed on the oxidized surfaces compared with the counterpart alloy 1# and alloy 3#. The high proportion of dense (Ni,Co,Cr)WO4 phase and the Ce2O2S2 third phase resistant to high-temperature oxidation can form a double obstacle to the diffusion of oxygen atoms and delay the kinetic process of oxidation reaction.