Good Oxidation Resistance Research Articles

The as-cast AlxCrTaTi refractory medium entropy alloys with good room-temperature mechanical properties and high-temperature oxidation resistance

Refractory medium entropy alloys (RMEAs) usually show good mechanical properties at high temperature. Unfortunately, their very poor room-temperature plasticity and high-temperature oxidation resistance still greatly limit their practical application. In this work, the room-temperature mechanical properties and high-temperature oxidation resistance of AlxCrTaTi RMEAs (x = 0, 0.15, 0.25, 0.35) are systematically studied. It is found that the AlxCrTaTi RMEAs exhibit very high yield strength of about 1700 MPa and plasticity of above 10%. For Al-bearing RMEAs, a composite oxide layer containing Al2O3 is formed on the alloy surface. Under the synergistic effect with the CrTaO4 oxide layer in the middle layer, Al0.25CrTaTi alloy possesses good oxidation resistance at 1000 ℃ for 100 h with the oxidation weight gain of only 7.3 mg/cm2.

Thermal stability, pore structure characteristics of char layer and ablation resistance mechanism of new thermal insulation composites based on polyphosphazene polymer

Polyphosphazene (PDPP) composites have emerged as a hot research topic in the field of low-density composite insulation materials because of their good thermal stability and flame retardancy. In this study, the ablative properties and mechanism of PDPP composites reinforced by fiber and functional fillers are studied. The test results show that PDPP composites have good thermal stability and oxidation resistance. The results of the oxyacetylene ablation test show that PDPP composites has strong ablation resistance, and its char layer has high structural strength, as well as high bonding strength with the material matrix. However, the thermal insulation performance of PDPP composites is weak. Based on the physical and chemical analysis of the composite material and the char layer, it is concluded that the excellent ablation resistance is mainly due to the high strength of the char layer, which bnefits from high char yield of polyphosphazene polymer and the formation of silicon phosphate. However, the high thermal conductivity of composite and char layer lead to poor thermal insulation performance.

SiO2-modified Y2Co8Fe9 multifunctional alloys with efficient microwave absorption, oxidation resistance and corrosion resistance

The application of a single metallic magnetic absorbing materials in harsh environments such as high temperature and corrosion reduces its absorption capacity significantly. Therefore, it is urgent to develop multifunctional composite materials with good absorption properties, oxidation resistance and corrosion resistance. In this work, SiO2-modified Y2Co8Fe9 (YCF) alloys with tunable tetraethyl orthosilicate content are prepared by the Stӧber method. The SiO2 coating efficiently enhances the microwave absorption properties due to the improved impedance matching characteristics. The SiO2 coating also provides effective physicochemical protection to prevent the alloys from oxidation and corrosion. Importantly, the YCF@SiO2-6 composite possesses enhanced microwave absorption properties with a minimum reflection loss (RLmin) of − 58.5 dB at 12.46 GHz with a thickness of 1.5 mm. The starting oxidation temperature of the YCF@SiO2-6 composite was 280 ℃ and 50 ℃ higher than that of the YCF and YCF@SiO2-2 samples, respectively. In addition, the corrosion resistance of the YCF@SiO2-6 composite in 3.5 wt% NaCl solution and hot and humid environment was tested by two different methods. The results indicate that the SiO2-modified sample shows good corrosion resistance. Therefore, this research provides a simple and practical method for the preparation of multifunctional composites in the field of electromagnetic wave absorption.

Compound purification of nickel base superalloy cutting waste through special cleaning agent attached to ultrasonic stirring

The GH4169 nickel-based superalloy is a type of alloy that exhibits excellent properties. It has high creep strength, fracture strength, as well as good corrosion resistance, fatigue resistance, and oxidation resistance under high-temperature conditions, allowing it to be widely used in the aerospace, nuclear reactor, and oil industries. However, it is challenging to process superalloys because of their high hardness and considerable processing wastes, such as cutting fluid. Many processing wastes cannot be directly used for remelting due to issues like surface stains. However, the production of GH4169 superalloys requires low carbon content for recycling, so the alloy scraps that meet the standard after pre-cleaning can be obtained. This study explores the ultrasonic cleaning effect of superalloy scraps with different liquid-solid ratios, cleaning times, and cleaning temperatures to obtain the optimal cleaning conditions of GH4169 superalloy scraps. The content of carbon in unwashed superalloy scraps is as high as 0.2%, far exceeding the carbon content of the alloy itself (0.015–0.036%). After ultrasonic cleaning at 60 °C for 30 min with a cleaning solution having a solid-liquid ratio of 1:2.5, the carbon content of the scraps decreased from over 0.2%–0.048%, and the decarburization rate reached above 77%. After remelting the cleaned scraps into alloy bars, the composition content and properties of the bars meet the production requirements. The cleaning mechanism is analyzed, and the cavitation effect, saponification, and emulsification mode in the ultrasonic cleaning process are explained. This paper positively promotes recycling GH4169 nickel-based superalloy waste to protect environmental resources.

Improvement of SiC/PyC coating on mechanical and anti-oxidation properties through biomimetic laminated structure design

To improve fracture toughness and oxidation resistance of SiC coating, we designed and prepared a SiC/PyC laminated coating with biomimetic laminated structure on carbon/carbon (C/C) composites by chemical vapor deposition (CVD) method. The microstructure, mechanical properties and oxidation resistance of the coating were investigated. The results showed that the laminated structure could effectively improve the toughness of SiC coating and avoid the formation of penetrating cracks, thus improved the oxidation resistance of coating. The weight loss of laminated SiC/PyC coated sample decreased 75.2 % compared with that of single SiC coated sample after oxidation at 1773 K. The good oxidation resistance and mechanical properties of SiC/PyC laminated coating were attributed to the toughening effect of laminated structure including crack deflection and interface debonding. Our work could bring beneficial enlightenment to improve the toughness of ceramic coating.

Ablation behavior of Cf/ZrC-SiC and Cf/SiC composites produced by precursor infiltration and pyrolysis combined with gaseous silicon infiltration

The ablation behavior of Cf/ZrC-SiC and Cf/SiC composites by a novel combined process was studied. The FLUENT calculation indicates high thermophysical gradients of oxyacetylene torch, which determines ablation behavior of the composites. The integrated effects of oxidation, evaporation and mechanical factor result in discontinuous SiO2 scale, thus causing severe ablation of Cf/SiC composites. As for Cf/ZrC-SiC composites, the joint action of ZrO2 and SiO2 bilayer structure provides good ablation and oxidation resistance. Nevertheless, a little erosion of Cf/ZrC-SiC composites occurs by the integrated effects of chemical and physical erosion, and the mechanical factor plays a more important role.

Oxidation behavior of Ti3SiC2 powder synthesized by using biochar, Si and Ti

Biochar was proposed as a novel carbon source for synthesizing Ti3SiC2 powder with high purity by a simple pressureless sintering at 1673 K, and Ti3SiC2 grains exhibited the typical nanolayered structure. The oxidation behavior of Ti3SiC2 powder showed the parabolic law during isothermal oxidation from 1273 K to 1473 K. Dense and continuous oxidation layer consisting of mixed TiO2 and SiO2 was formed rapidly on the surface of Ti3SiC2 particles as a diffusion barrier, which effectively retarded the inward diffusion of oxygen, conferring good oxidation resistance of the powder.

Grain boundary segregation induced strong UHTCs at elevated temperatures: A universal mechanism from conventional UHTCs to high entropy UHTCs

Ultra-high temperature ceramics (UHTCs) exhibit a unique combination of excellent properties, including ultra-high melting point, excellent chemical stability, and good oxidation resistance, which make them promising candidates for aerospace and nuclear applications. However, the degradation of high-temperature strength is one of the main limitations for their ultra-high temperature applications. Thus, searching for mechanisms that can help to develop high-performance UHTCs with good high-temperature mechanical properties is urgently needed. To achieve this goal, grain boundary segregation of a series of carbides, including conventional, medium entropy, and high entropy transition metal carbides, i.e., Zr0.95W0.05C, TiZrHfC3, ZrHfNbTaC4, TiZrHfNbTaC5, were studied by atomistic simulations with a fitted Deep Potential (DP), and the effects of segregation on grain boundary strength were emphasized. For all the studied carbides, grain boundary segregations are realized, which are dominated by the atomic size effect. In addition, tensile simulations indicate that grain boundaries (GBs) will usually be strengthened due to segregation. Our simulation results reveal that grain boundary segregation may be a universal mechanism in enhancing the high-temperature strength of both conventional UHTCs and medium/high entropy UHTCs, since GBs play a key role in controlling the fracture of UHTCs at elevated temperatures.

Effect of Fe on the Hydrogen Production Properties of Al-Bi-Sn Composite Powders.

Fe additives may play an important role in the preparation of aluminum-based hydrolysis hydrogen powder, with high hydrogen yield, low cost, and good oxidation resistance. Therefore, it is necessary to ascertain the effect of Fe on the hydrogen production performance of Al-Bi-Sn composite powders. According to the calculated vertical cross-section of the Al-10Bi-7Sn-(0~6)Fe (wt.%) quasi-binary system, Al-10Bi-7Sn-xFe (x = 0, 0.5, 1.5, 3) wt.% composite powders for hydrogen production were prepared by the gas-atomization method. The results showed that the Al-10Bi-7Sn-1.5Fe (wt.%) powder exhibited an extremely fast hydrogen generation rate at 50 °C, which reached 1105 mL·g−1 in 27 min in distilled water, 1086 mL·g−1 in 15 min in 0.1 mol·L−1 NaCl solution, and 1086 mL·g−1 in 15 min in 0.1 mol·L−1 CaCl2 solution. In addition, the antioxidant properties of these powders were also investigated. The results showed that the hydrogen production performance of the Al-10Bi-7Sn-1.5Fe (wt.%) powder could retain 91% of its hydrogen production activity, even though the powder was exposed to 25 °C and 60 RH% for 72 h. The addition of Fe not only promoted the hydrogen generation rate of the Al-Bi-Sn composite powders, but also improved their oxidation resistance. The Al-10Bi-7Sn-1.5Fe (wt.%) composite powder shows great potential for mobile hydrogen source scenarios with rapid hydrogen production.

Microstructure and mechanical response of dissimilar joint of ferritic interstitial-free steel to austenitic low-density steel produced by diffusion bonding

Lightweight Fe–Mn–Al–C steels, also referred as low-density steels (LDS), have gained significant importance in the recent past owing to their reduced density, high strength and ductility, along with good oxidation resistance at elevated temperatures. The present study is aimed at exploring the feasibility of solid-state joining of LDS to the other prominent ferrous alloys, for example, interstitial-free steel (IFS), in order to extend their applications. In the present work, diffusion bonding has been attempted to produce IFS-to-LDS joints with and without the application of nickel (Ni) interlayer. Diffusion bonding is performed at two different temperatures of 850 °C and 950 °C for 30 min at the bonding pressures of 10, 20 and 30 MPa under high vacuum conditions. The interfacial microstructures of the joints are examined using an optical microscope and scanning electron microscope in conjunction with energy dispersive spectroscopy and electron backscattered diffraction. Microhardness and nanoindentation measurements across the interface and shear tests are performed to evaluate the interfacial bond strength of the joints. The joint produced with the application of Ni interlayer at 950 °C under 30 MPa bond pressure exhibited superior shear properties with a maximum shear strength of ∼340 MPa. The formation of stable oxides resulting, especially by diffusion of aluminum from LDS to the faying surfaces is found to be detrimental to establish a good interface at lower bonding parameters. The application of higher bonding pressure and Ni interlayer along with enhanced diffusional activities from LDS to IFS within the austenite phase are found to be effective in achieving a sound joint. The metallurgical aspects involved in the formation of the reaction products and subsequently, the influence of the evolved interface microstructure on the mechanical response of the joints are discussed in-detail.

A SiCN Thin Film Thermistor Based on DVB Modified Polymer-Derived Ceramics.

Carbon-rich SiCN ceramics were prepared by divinylbenzene (DVB)-modified polysilazane (PSN2), and a high-conductivity SiCN thin film sensor suitable for medium-low temperature sensing was fabricated. The modified liquid precursors were patterned by direct ink writing to produce SiCN resistive grids with line widths of several hundreds of micrometers and thicknesses of several micrometers. The introduction of DVB not only increases the critical thickness of SiCN ceramics several times, but also significantly improves the conductivity of SiCN, making it meet the conductivity requirements of sensing applications in the mid-low temperature range. The electrical conductivity and microstructure of DVB-modified SiCN ceramics were studied in detail. In the temperature range of 30~400 °C, the temperature resistance performance of DVB modified SiCN resistance grid was measured. The SiCN ceramics with low DVB content not only have excellent electrical conductivity, but also have good oxidation resistance.

Anchoring Highly Sulfonated Hyperbranched PBI onto oPBI: Fast Proton Conduction with Low Leaching

To achieve fast proton conduction with low leaching of the proton conductor, hyperbranched polybenzimidazole with abundant terminal diamino groups was synthesized and highly sulfonated to yield the cross-linkable proton conductor SHBPBI. A high-temperature proton exchange membrane (HTPEM) was prepared with ether containing polybenzimidazole (oPBI) and triallyl isocyanurate (TAIC). TAIC formed covalent bonds with N–H bonds in oPBI and SHBPBI, and effectively anchored soluble SHBPBI onto the oPBI-TAIC network without sacrificing proton-conducting sulfonic acid groups. oPBI-TAIC-SHBPBI exhibited good thermal stability, mechanical property, dimensional stability, oxidative resistance, membrane selectivity, and low methanol/H2/O2 crossover. The proton conductivity of oPBI-TAIC(5%)-SHBPBI(50%) achieved was 0.147, 0.074, and 0.034 S cm–1 at 100%, 50%, and 0 RH at 180 °C, respectively. The conductivity of oPBI-TAIC(5%)-SHBPBI(50%) at 0 RH remained 97.1% after washing with water for 96 h, indicating low leaching of the soluble proton conductor SHBPBI. The composite membranes exhibited potential application in HTPEM fuel cells and direct methanol fuel cells (DMFCs).

A promising new class of high-entropy ceramics: High-entropy oxycarbides with good oxidation resistance

(Hf0.25Zr0.25Nb0.25Ti0.25)(C0.5O0.5) high-entropy oxycarbides (HECO-1) with good oxidation resistance, as a promising new class of high-entropy ceramics, were synthesized by a facile carbothermic reduction method for the first time. The results showed that the as-synthesized HECO-1 samples had the single-phase rock-salt structure and high compositional uniformity. Compared to the as-synthesized (Hf0.25Zr0.25Nb0.25Ti0.25)C high-entropy carbides, the as-synthesized HECO-1 samples possessed the higher initial oxidation temperature and slower oxidation rate to show the better oxidation resistance, making them the promising applications in extreme environments, which was attributed to their higher oxidation activation energy and Gibbs free energy of oxidation reaction.

High vacuum arc ion plating Cr film for promoting high temperature applicability of Cu

Copper-made electrical coils are normally subject to severe oxidation above 300 °C in air and thus are less applicable at elevated temperatures. In this work, a coarse-grained thin Cr film was prepared by high-powered high vacuum arc ion plating for protecting Cu against oxidation and suppressing the abnormal Cr film/Cu interdiffusion at 600 °C. The well-adherent thin Cr film exhibited good oxidation resistance and more importantly almost no interdiffusion with Cu, showing the superior thermal stability of the Cr film/Cu system. It demonstrates great potentials of the Cr film for promoting high temperature applicability of Cu.

Insights into the surface pretreatment on the oxidation behavior of anodized TiAl alloy

The influence of surface pretreatment on the oxidation performance of the anodized TiAl alloy was investigated. Before anodization in NH4F containing ethylene glycol, TiAl alloy was sand blasted or ground by SiC paper. Results showed that the humps on the rough surface serve as crystallographic templates for the nucleation of the isostructural α-Al2O3 at the initial stage of oxidation. The derived Al2O3 act as the crystal nuclei for the formation of continuous Al2O3 oxide scale during thermal exposure, therefore providing good oxidation resistance. The surface roughness acts a key role to improve the oxidation resistance of the anodized TiAl alloy.

Porous MoAlB ceramic via reactive synthesis: Reaction mechanism, pore structure, mechanical property and high temperature oxidation behavior

Porous MoAlB ceramics were synthesized by an activation reaction sintering technique using Mo, Al and B powders as starting materials. The phase transformation, pore forming mechanism and the development of microstructure of porous MoAlB were discussed. MoAlB in pure phase was obtained at 1000 °C. The effects of Kirkendall effect and phase transformation are related to the changes of pore size, open porosity and expansion of porous MoAlB during the sintering process. The mechanical properties test shows that porous MoAlB ceramic has excellent processability and tensile strength. The oxidation test exhibits that porous MoAlB ceramic exhibits good oxidation resistance at high temperatures.

Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings

Multicomponent carbides have gained interest especially for ultra-high temperature applications, due to their ceramic hardness, good oxidation resistance and enhanced strength. In this study the phase formation, stability and mechanical properties of (HfNbTiVZr)C multicomponent carbide coatings were investigated. Phase stability was predicted by the CALPHAD (CALculation of PHAse Diagrams) methods. This revealed that the multicomponent solid solution phase is only stable at elevated temperatures, namely above 2400 °C. At lower temperatures a phase mixture was predicted, with a particular tendency for V to segregate. Magnetron sputtered thin films deposited at 300 °C exhibited a single NaCl-type multicomponent carbide phase, which attributes to the kinetic stabilisation of simple structures during thin film growth. Films deposited at 700 °C, or exposed to UHV annealing at 1000 °C, however, revealed the decomposition of the single-phase multicomponent carbide by partial elemental segregation and formation of additional phases. Thus, confirming the CALPHAD predictions. These results underscore the importance of explicitly considering temperature when discussing the stability of multicomponent carbide materials, as well as the applicability of CALPHAD methods for predicting phase formation and driving forces in these materials. The latter being crucial for designing materials, such as carbides, that are used in applications at elevated temperatures.

Molecular dynamic simulations of modeling aluminum-based composite nanoparticle in liquid Cellulose dinitrate decamer sol

Aluminum nanoparticle (ANP) in liquid Cellulose dinitrate decamer sol was investigated by ReaxFF molecular dynamics simulations. The mechanism of nitrocellulose (NC) single chain adsorption was researched as a chemisorption process. New Al–O bonds are formed by dehydrogenation and denitrification of the nitrate ester groups. The adsorbed part of the NC chain drags other parts to the surface as a horizontal adsorption state. We also simulated the processes of liquid Cellulose dinitrate decamer sol (ethanol, diethyl ether, and NC three components) coating the ANPs at different temperatures. The results indicate that the organic coating near surface is mainly consisted of ethanol and diethyl ether molecules. The NC chains are adsorbed on the ANPs surface in two states, including the horizontal adsorption or the nearly vertical adsorption. Heating can increase the coating rate without significantly changing the composition of the coating. Finally, the oxidation simulation shows that the organic layer can maintain good stability and oxidation resistance.

High temperature oxidation and hot corrosion behaviors of Fe65.7Ni11.7Ti1Mo6.6Co15 high entropy alloy

Understanding the surface oxidation and hot corrosion properties of the Fe65.7Ni11.7Ti1Mo6.6Co15 high entropy alloy (HEA) at high temperatures and hot corrosion media could provide useful insights into designing the high performance of the metallic materials, which is indispensable for its wide applications. Herein, at about 1923 K, the HEA was prepared by vacuum induction melting with five principal metals (Fe, Ni, Ti, Mo, and Co) in the solid-solution form. The high temperature oxidation tests at 823 K, 923 K, and 1023 K, and the hot corrosion tests using mixtures of NaCl and Na2SO4 as the hot corrosion media at 923 K were carried out, respectively. High temperature oxidation and hot corrosion behaviors were investigated via surface and cross-section morphologies observation, oxidation and corrosion products tests, and chemical composition distribution maps analysis. The effect of temperature on the oxidation resistance, as well as the effect of the content of NaCl in the mixed salt medium on the hot corrosion resistance were revealed. The results show that the HEA exhibited good high temperature oxidation resistance at 923 K according to mass gain and products after oxidation. The higher content of NaCl in the mixed salt medium can bring more intense hot corrosion. In addition, more oxygen and molten salts can be migrated via cracks and dense pores, which is not conducive to enhancing the high temperature oxidation resistance and hot corrosion resistance.

Low-carbon CeOx/Ru@RuO2 nanosheets as bifunctional catalysts for lithium-oxygen batteries

Lithium-oxygen (Li-O2) batteries are facing challenges in capacity, cycling stability, and kinetics for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Advanced catalysts should have a high and bifunctional catalytic activity for ORR and OER. Moreover, the trade-off carbon in catalysts should have good oxidation resistance and high electronic conductivity and be used in a tiny amount. Up to now, it is still a challenge. Therefore, this work introduces a low-carbon CeOx/Ru@RuO2 nanosheet as efficient cathode catalysts for Li-O2 batteries and studies the preparation and working mechanisms using a variety of characterization and electrochemical techniques. The air oxidation treatment oxidizes Ru into Ru@RuO2 and simultaneously removes unstable C into CO2, leaving a tiny amount of stable carbon. CeOx/Ru@RuO2 has enormous mesopores, well-distributed sub-5 nm CeOx and Ru@RuO2 nanocrystals, a tiny amount of anti-oxidation carbon (1.2 %), and a high specific surface area of 159.3 m² g−1. These aspects optimize the Li-O reaction and regulate the Li2O2 nucleation to form uniform and ultrathin Li2O2 nanoflakes. As a result, the ORR and OER overpotentials are only 0.17 V and 0.45 V, respectively. This work provides a novel material combination and structure design for developing bifunctional catalyst materials in Li-O2 batteries.