Improved Oxidation Resistance Research Articles

Investigating the Replacement of Nickel-based Superalloys with Niobium-Based Superalloys in the New Generation of Turbine Blades in the Aero-space Industry

To improve the thermal properties of superalloys or replacing them with new materials is necessary to increase engine efficiency. When considerable progress in superalloys is unlikely, researchers started to turn their attention to alternative materials. Metallic silicide alloys are cheaper choices for increasing engine efficiency. The melting point for molybdenum and niobium silicide is much higher than the melting point of the current alloys. This shows these alloys have the potential to increase temperature in gas turbine engines. These alloys have poor oxidation resistance. Improving oxidation resistance of each alloy system is a significant step toward a new material for turbine blades. To improve oxidation resistance in these alloys, many experiments have been done in which alloy elements such as Ti, Cr, Al, Zr, Ta, and Sn have been used. According to these experiments, it can be concluded that Zr is practically ineffective and it cannot improve oxidation resistance in alloys. In some temperatures, Ta is even harmful for oxidation resistance. Sn has the best function to increase oxidation resistance by forming a rich layer of Sn, oxygen penetration into depth is prevented. Despite these alloy elements, they are not enough resistant to oxidation to function in higher temperatures. To be replaced by nickel-based superalloys in gas turbine blades in the aerospace industry they need to have higher oxidation resistance.

In-situ preparation of Ni@ZrO2 nanocapsules powder by DC arc plasma for internal electrode of MLCC

Zirconium oxide-coated Ni nanocapsules (Ni@ZrO2 NCs) were in-situ fabricated by DC arc plasma in a nitrogen atmosphere. The co-evaporation of a target mixture consisting of coarse ZrO2 and Ni powders resulted in the formation of Ni@ZrO2 core-shell nanocomposites (NCs). The high energy states of excited ions (Ni3+, Zr4+, O2−, N2+, etc.) within the arc plasma region were recorded in real time by online optical emission spectroscopy (OES), which becomes visible evidences of the energy conditions for the fabrication of Ni@ZrO2 NCs. These nanocapsules underwent preferential formation of zirconium oxide species based on the oxygen potential rule, followed by the nucleation and subsequent growth processes. The Ni@ZrO2 NCs exhibited improved oxidation resistance, with an onset temperature for sintering approximately 40 °C higher than that of pristine Ni nanoparticles (NPs). Additionally, these NCs displayed an appropriate shrinkage rate, with a volume change of about 7.1% at 1200 °C. The symbiotic relationship between the ZrO2 shell and the Ni core within each nanoparticle suggests enhanced interfacial stability, rendering these NCs a promising material for the advancement of multi-layer ceramic capacitors (MLCCs).

Toughened bulk high-entropy diborides with high hardness and enhanced oxidation resistance via SiC whiskers

The fracture toughness and oxidation resistance are crucial factors affecting the practical applications of high-entropy diboride ceramics (HEBs). In this study, silicon carbide whiskers (SiCw) were introduced as a reinforcement for HEBs for the first time. To achieve a uniform dispersion of SiCw within the HEB powders, a combination of simultaneous ultrasonic dispersion, mechanical agitation, and freeze-drying technology was employed. Consequently, a series of composites, (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2-nSiCw (n = 0–20 vol%), were densified by spark plasma sintering. The effect of SiCw on the microstructure and mechanical properties of the HEBs were studied, as well as the toughening mechanism involved. The results revealed that the introduction of SiCw led to grain-size refinement in (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2, along with significant improvements in relative density, hardness, fracture toughness, and oxidation resistance. The relative density, hardness and fracture-toughness of (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2-SiCw composites exhibited an initial increase followed by a decrease with increasing SiCw content. Specifically, the (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2–15 vol% SiCw composite simultaneously obtained the highest hardness of 25.6 GPa and fracture-toughness of 4.8 MPa·m1/2, representing a 26% improvement compared to (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2 ceramics.

The new Iridium-Hafnium-Aluminum alloy thin films with excellent mechanical properties and oxidation resistance

Improving oxidation resistance has long been a challenge for hot end components in high temperature environments. We have fabricated a series of IraHfbAlc (at. %) alloy thin films by multi-targeted direct current magnetron sputtering (DC-MS) and have thoroughly investigated the microscopic mechanism of the films. More importantly, we for the first time prepared IraHfbAlc alloy thin films with a preferred (111) orientation substitution solid solution, which exhibits excellent mechanical properties and oxidation resistance. The minimum surface roughness (Ra) value of the IraHfbAlc alloy films was 0.7 nm, while the maximum hardness (H) and elastic modulus (E) exceeded 20 GPa and 330 GPa, respectively. The oxidized volatility of the Ir in the films was only 0.11 μm/h at 1300 °C (lower than most previously reported values, such as 0.5 μm/h), which greatly improved the lifetime of the film. Confirmation that lattice distortion induces the refinement of crystal-like order (CLO) in thin films, and solves the mystery of enhanced oxidation resistance. The findings provide important insights into the design of Ir-containing alloy coatings and offer new ideas in the field of high-temperature protection.

Effect of coatings on oxidation behavior of a fourth generation Ni-based single crystal superalloys at ultra high temperature

PtAl and MCrAlY coating were prepared on the fourth generation single crystal superalloy. The isothermal oxidation tests of superalloys with different coatings were performed at 1150 °C and 1200 °C in a muffle furnace with static air for 500 h. The isothermal oxidation behavior and mechanism of two coatings at 1150 °C and 1200 °C was investigated. MCrAlY coating improved oxidation resistance by forming adhesive oxide scales with pegs, and PtAl coating formed dense and coherent oxide scales on surface to hinder the diffusion of oxygen. Compared with two coatings, a smaller oxidize increasing weight of PtAl coating (0.54 mg/cm2) than MCrAlY coating (2.48 mg/cm2) indicated that PtAl coating presented a better oxidation resistance during oxidation test at ultra high temperature, although a significant interdiffusion behavior occurred between PtAl coating and substrate. Besides, the interactive behavior between Ru and coatings was also investigated. Ru in fourth generation single crystal superalloy could diffuse into β-NiAl phase of coatings, maintaining the integrity of coatings. The major difference between MCrAlY coating and PtAl coating came in the amounts of β-NiAl phase, which leading to the difference on the oxidation resistance between MCrAlY and PtAl. The mechanism about influence of temperature on the oxidation property on bare alloy, MCrAlY-DD91 and PtAl-DD91 was also discussed. Ultra high temperature would promote more elements to participate in the reaction with oxygen, change the compositions of oxide scale and phases, resulting to the spallation of oxide scale and decrease of oxidation resistance.

Carbon nanotube mat/boron nitride composite materials for aerospace applications

Boron nitride (BN) is a coating material that can overcome the shortcomings of CNT mat. In this study, a CNT mat-BN composite was fabricated in a layer-by-layer manner using chemical vapor deposition. Raman, Fourier transform infrared, and electron energy loss spectroscopy analyses revealed that the coating layer consists of sp2-hybridized BN. The CNT mat-BN composite had improved oxidation resistance owing to the oxygen-blocking capability and stability of the coating layer. Moreover, the composite exhibited neutron shielding ability owing to the well-dispersed B10 atoms in BN. Because CNT mat-BN was chemically strongly bonded owing to the penetration of BN and the subsequent formation of CN covalent bonds, the slippage of CNT bundles under high stress was prevented, enhancing the tensile strength. BN coating on a CNT mat provided increased tensile strength, neutron-shielding ability, and high oxidation resistance.

Hybrid HfC‐SiCN matrix for improved oxidation resistance of carbon fiber–reinforced mini‐composites

AbstractHafnium carbide (HfC) is an ultrahigh‐temperature ceramic with high melting point, chemical stability, hardness, and wear resistance. However, its low fracture toughness and poor thermal shock resistance limit its structural applications in extreme environments. In this study, co‐curing of liquid precursors was carried out prior to complete pyrolysis of individual polymeric precursors. First, HfC preceramic polymer precursor was cured, followed by silicon carbonitride (SiCN) precursor curing on a 2D carbon fiber (CF) cloth using the drop‐coating process. The infiltrated CFs were pyrolyzed at 800°C to achieve CF/HfC‐SiCN ceramic mini‐composites. The cross‐linked precursor‐to‐ceramic yield was observed to be as high as 65% when the procedure was carried out in an inert environment. Although stable up to 1200°C, CF/HfC‐SiCN samples demonstrated susceptibility to oxidation at 1500°C in ambient air. The oxidation of HfC in the presence of SiC leads to the formation of a hafnium‐containing silicate (HfxSiyOz) along with hafnia (HfO2). This compound of silicate and hafnia limits oxygen diffusion better than SiO2 and HfO2 individually. The incorporation of SiCN in HfC ceramic led to improved phase stability compared to a neat HfC system. The results of this study also show that the use of liquid‐phase precursors for HfC and SiCN in the polymer‐infiltrated pyrolysis method is a promising approach to fabricating high‐temperature structural ceramic matrix composites with good oxidation resistance.

Self-densification behaviors and oxidation resistance properties of a slurry-derived ZrB2-SiC coating with kyanite additive

The great advantages of component designability, operation convenience, and cost reduction make the slurry-sintering method promising for preparing oxidation resistant coatings. However, the porous structure caused by the volatilization of liquid in the slurry and shrinkage of particles in the pressureless sintering limits its practical and wide application. Herein, a dense ZrB2-SiC coating with improved oxidation resistance was fabricated via a slurry-sintering method on C/SiC composites by introducing kyanite into the slurry. The self-densification of the coating is achieved due to the volume expansion of 26.1 % related to the irreversible thermal transformation from kyanite to mullite during sintering. The resultant dense coating with a thickness of 150 μm shows the good interfacial bonding strength of 19.2 MPa and the low weight changes of 1.7 %, −0.6 %, and −1.7 % at 800 °C, 1000 °C, and 1200 °C for 40-h oxidation, respectively.

Effect of Binder on Oxidation Properties of Tungsten Carbides: A Review by a Conceptual Classification Approach

This study presents a conceptual classification scheme to review the literature on improving the oxidation resistance of tungsten carbide by modifying the binder. The first parts of the article are dedicated to the specification of the databases, the search method, and the description of the criteria chosen to classify the articles. Then, the data collected are presented in statistical graphs according to the proposed classification scheme. The data analyzed show that most of the significant improvements in oxidation resistance are achieved with advanced production processes, especially HIP and SPS, which eliminate porosity to a very high degree. In addition, statistical studies showed that the use of new replacement binders, Ni3Al, Fe–based alloys, FeAl, and Al2O3, improved the oxidation properties in 75–100% of cases. Meanwhile, the use of high–entropy alloys (HEAs) as cermet binders may be the subject of future research for oxidation, given the recently published results of good mechanical properties.

Improved oxidation resistance while maintaining slag corrosion resistance of MgO–SiC–C refractories with moderate amounts of liquid phase

AbstractMgO–SiC–C refractories with superior hot strength, oxidation resistance and slag resistance have potential to become substitute refractories for matte smelting furnace. In the present work, the influence of glass powder addition on phase compositions, hot strength, oxidation resistance, and slag resistance of MgO–SiC–C refractories was investigated. The liquid phase introduced by glass powder filled the pores, blocking the channel for the ingress of the oxygen and thus improving the oxidation resistance. Although the oxidation resistance of such refractories was improved with 1–3 wt% glass powder addition, their hot strength and slag corrosion resistance decreased when the glass powder content was 2–3 wt%. To balance the mechanical properties, oxidation resistance and slag resistance, low amount glass powder addition (1 wt%) was considered better choice.

The Effect of Nb, Ta, and Ti on the Oxidation of a New Polycrystalline Ni-Based Superalloy

The effect of variations in Nb, Ta, and Ti concentrations in exchange for Al on the oxidation resistance of a new polycrystalline Ni-based superalloy (C19) was studied in air at 800 °C for up to 1000 h. An external scale of Ti-doped Cr2O3 and a sub-scale of discontinuous Al2O3 intrusions formed on the surface of all the studied alloys. Contrary to other reports, increasing the Nb concentration improved the oxidation performance and may have promoted the formation of a CrTaO4 layer, thereby reducing oxygen ingress. The addition of Ta also significantly improved oxidation resistance and reduced the depth of the Al2O3 intrusions. Increasing the Ti concentration did not significantly affect the oxidation performance, potentially due to the relatively low Ti concentrations investigated. Several of the studied alloys with modified Ta and Ti concentrations showed regions of continuous Al2O3 scale formation, suggesting that the compositions are in a transition regime between Cr2O3-forming and Al2O3-forming behaviour. The findings suggested that part of the Ti content in C19 could potentially be replaced with Nb, Ta and/or other elements to further enhance oxidation resistance and other desirable properties. Overall, the insights gained could serve as a guide to optimise the composition of C19 and similar alloys for enhanced oxidation resistance.

A ZrB2-SiC(Al) coating with improved oxidation resistance for C/C composites: Design, experimental verification and oxidation mechanism

In order to improve the oxidation resistance of ZrB2-SiC coating, Al2O3 dopant was introduced to modify the structure of oxygen-inhibiting glassy layer. Al2O3-doped ZrB2-SiC (ZrB2-SiC(Al)) coating was designed, optimized and prepared by spark plasma sintering. Microstructure evolution and oxidation mechanism were investigated by experiment and first-principles calculation. Compared with ZrB2-SiC coating, ZrB2-SiC(Al) coating showed a significantly improved oxidation resistance. Characterization and calculation results indicated that the superior oxidation resistance could be ascribed to the higher bridging oxygen content, the improved stability of glass structure, and the decreased oxygen diffusion rate of glassy layer due to the increased solubility of ZrO2.

High temperature oxidation behaviors of C/C composites with SiOC coatings

The oxidation behaviors of C/C composites with various silicon oxycarbide (SiOC) coatings prepared at various deposition temperatures (1300 - 1513 K) were studied. The SiOC coating improved the oxidation resistance of C/C composites by forming dense SiO2 glass, but such an improvement was sensitive to the deposition temperature. The SiOC coatings prepared at low temperatures exhibited limited oxidation resistance improvement given the appearance of penetrating cracks, fundamentally caused by their thin, amorphous (high elastic modulus), dense, and brittle characteristics. The SiOC coatings prepared at high temperatures had thick, polycrystalline (low elastic modulus), loose, and resilient structures, thus exhibiting higher oxidation resistance.

Theoretical study of the effects of alloying elements on TiO2/Ti2AlNb interface adhesion properties.

Ti2AlNb-based alloys are expected to be applied in the manufacture of parts of aeroengines to achieve the goal of increasing the thrust-to-weight ratio. However, the poor high temperature oxidation resistance of these alloys may hinder their applications. Alloying has been proven to be effective in improving oxidation resistance properties. However, the selection of alloying elements and their influence mechanisms are rarely studied. The TiO2/Ti2AlNb interface bonding interactions and the effects of alloying elements of Si, Sc, Y, Zr, Mo and Hf were investigated via first principles calculations. The separation energy and electronic structure were studied to explore the bonding interactions between the oxide scale and Ti2AlNb matrix. When Zr and Hf are used to replace Al, the bonding properties of the TiO2/Ti2AlNb interface are improved. The tensile and shear deformations of the interfacial zones are applied to study the influence of alloying elements on the TiO2 oxide spalling on Ti2AlNb. The tensile strength is increased by more than 2 GPa when Nb is substituted by the Sc, Zr and Hf elements. Therefore, Sc, Zr, and Hf are beneficial for inhibiting oxide spalling and will have great potential to improve the oxidation resistance properties.

High-Temperature Oxidation Behavior of FeCoCrNi+(Cu/Al)-Based High-Entropy Alloys in Humid Air

Previous studies showed some transition metal high-entropy alloy (HEA) compositions can have good oxidation resistance in air up to 800 °C. Four equiatomic HEAs have been developed based on FeCoCrNi with additions of Mn, Cu, Al or Al+Cu. The oxidation behavior of these HEAs was compared in humid (10 vol.% H2O) air at 800 °C for 100–500 h to investigate the influence of water vapor on the oxidation mechanisms. The Cu- and Al-containing alloys exhibited improved oxidation resistance over the Mn composition. For the Cu-containing alloy, a local attack of the Cu-rich phase was observed, which formed an Fe/Ni/Co/Cr spinel that was surrounded by Cr2O3. This oxide was thicker for the humid air atmosphere when compared to dry air, and the transition of the Cu oxide to the spinel was accelerated. The Al-containing HEA formed a thin Al2O3 scale with humidity suppressing AlN formation and forming a smoother oxide layer. The Al+Cu composition had the highest overall oxidation resistance (minimal local attack, no nitridation) and also showed a smooth oxide scale topography under humid air oxidation as opposed to a plate-like, rougher scale under dry air.

Nanoscale friction of high entropy alloy sulfide thin films in comparison with molybdenum disulfide

We present nanoscale friction measurements performed on sputter-deposited high entropy alloy (HEA) sulfide thin films [(VNbTaMoW)S2] via atomic force microscopy. The results reveal (i) the influence of deposition time on the film morphology and (ii) the presence of isolated areas of low friction on film surfaces. We compare the friction results on HEA sulfide thin films with those on a prototypical solid lubricant, sputter-deposited molybdenum disulfide (MoS2), and find that they are superior in terms of lubricative performance. Variable temperature x-ray diffraction, performed up to 973 K, reveals that HEA sulfide thin films exhibit improved oxidation resistance when compared with MoS2 films. Combined, our results show that HEA sulfide thin films have considerable potential as oxidation-resistant solid lubricant coatings.

Tuning Mo/W ratio to improve high temperature oxidation resistance of single crystal nickel base superalloys

The effect of different Mo/W ratios of three single crystal nickel base superalloys on the oxidation behavior was investigated at 1100 °C. Both isothermal and cyclic oxidation tests showed that increasing Mo/W ratio corresponds to lower weight change and improved resistance. The microscopic observation uncovers that the harmful effect of Mo is limited by the dense Al2O3 scale. In contrast, excessive W leads to fast growth of interlayer and its premature spallation. This research proposes and verifies a new way to improve oxidation resistance of alloy, namely, balancing the harmful effect of refractory elements.

Rapid Experimental Screening of High‐Entropy Diborides for Superior Oxidation Resistance

AbstractDue to the huge composition space, composition screening is of great importance to the optimization of high‐entropy diborides (HEBs) with exceptional oxidation resistance. However, related studies are lacking. Here, a novel rapid, effective strategy to fully screen the compositions on the oxidation resistance of HEBs is proposed. Specifically, the synthesis of the equiatomic 1‐ to 9‐cation multicomponent diborides of the IVB, VB, and VIB groups in seconds via an ultrafast ultrahigh‐temperature synthesis technique is realized. Subsequently, combined with the thermogravimetric analysis and first‐principles calculations, the roles of incorporated elements are systematically explored. The results show that Zr, Cr, Ta, Nb, and W elements are the key to the improved oxidation resistance of HEBs, while Ti, Mo, and V elements are destructive. In particular, the positive roles of metal elements are mainly attributed to the partial dissolution of the generated metal oxides into the generated B2O3 glass, which can improve the viscosity of B2O3 and thus enhance its high‐temperature stability and reduce the oxygen diffusion rate, as confirmed by the first‐principles calculations. This study paves a way to rapidly screen the elements in HEBs, which can be a guide for further anti‐oxidation designs.

Anomalous Mitigation in Phase Evolution Impacting Thermal Stability in a Rapidly Solidified AA5182 Al–Mg Alloy via Continuous Thin‐Strip Casting

This study, for the first time, reports an anomalous phase evolution and its impact on the thermal and oxidation behavior of rapidly solidified AA5182 Al–Mg alloy strip fabricated using a novel thin‐strip (TS) continuous casting technique. The microstructural analysis reveals a through‐thickness gradient microstructure of distinct types, morphology, and fractions of nonequilibrium Al–Mn–Fe intermetallic and Al–Mg eutectic phases. The rapid solidification experienced in TS casting effectively mitigates the formation of phases, particularly with the Al–Mg (β‐Al3Mg2) eutectic, being nearly absent from the near‐surface regions. The total fraction of formed phases is considerably lower than that in the slowly cooled direct‐chill counterpart. The solute macrosegregation also shows an inverse Mg segregation profile toward the strip surface primarily due to a higher degree of matrix supersaturation closer to the strip surface. Modeling of solidification successfully predicts the influence of cooling rate on the fractions of the nonequilibrium eutectic phase, agreeing well with the experimental data obtained from image analysis. Heat treating the samples over a broad temperature range unveiled unexpected improvements in oxidation resistance and excellent thermal stability, attributed to the absence of the eutectic β‐phase in subsurface regions. The research findings have practical implications for improving the properties of sheet Al–Mg alloys.

Insight into the effect of Ti substitutions on the static oxidation behavior of (Hf,Ti)C at 2500 ​°C

Hf-based carbides are highly desirable candidate materials for oxidizing environments above 2000 ​°C. However, the static oxidation behavior at their potential service temperatures remains unclear. To fill this gap, the static oxidation behavior of (Hf, Ti)C and the effect of Ti substitutions were investigated in air at 2500 ​°C under an oxygen partial pressure of 4.2 ​kPa. After oxidation for 2000 ​s, the thickness of the oxide layer on the surface of (Hf, Ti)C bulk ceramic is reduced by 62.29 ​% compared with that on the HfC monocarbide surface. The dramatic improvement in oxidation resistance is attributed to the unique oxide layer structure consisting of various crystalline oxycarbides, HfO2, and carbon. The Ti-rich oxycarbide ((Ti, Hf)CxOy) dispersed within HfO2 formed the major structure of the oxide layer. A coherent boundary with lattice distortion existed at the HfO2/(Ti, Hf)CxOy interface along the (111) crystal plane direction, which served as an effective oxygen diffusion barrier. The Hf-rich oxycarbide ((Hf, Ti)CxOy) together with (Ti, Hf)CxOy, HfO2, and precipitated carbon constituted a dense transition layer, ensuring favorable bonding between the oxide layer and the matrix. The Ti content affects the oxidation resistance of (Hf, Ti)C by determining the oxide layer's phase distribution and integrity.