Oxidation Resistance Properties Research Articles

Densification of Ceramic Matrix Composite Preforms by Si2N2O Formed by Reaction of Si with SiO2 under High Nitrogen Pressure. Part 2: Materials Properties

Ceramic matrix composites (CMCs) have been prepared and optimized as already described in part I of this paper. The fibrous preform made of Hi-Nicalon S fibers was densified by a matrix composed of Si2N2O prepared inside the CMC by reacting a mixture of Si and SiO2 under high nitrogen pressure. This part describes the oxidation resistance and mechanical properties of the optimized CMC. The CMC submitted to oxidation in wet oxygen at 1400 °C for 170 h exhibited an oxidation gradient from the surface to almost the center of the sample. In the outer part of the sample, Si2N2O, Si3N4 and SiC were oxidized into silica in the cristobalite-crystallized form. The matrix microstructure looks similar to the original one at the center of the sample, while at the surface large pores are observed and the fiber/matrix interphase is consumed by oxidation. The elastic modulus and the hardness measured at room temperature by nano-indentation are, respectively, 100 and 8 GPa. The elastic modulus measured at room temperature by tensile tests ranges from 150 to 160 GPa and the ultimate yield strength from 320 to 390 MPa, which corresponds to a yield strain of about 0.6%. The yield strength identified by acoustic emission is about 40 MPa.

Oxidization resistance and sorption properties of oleogels as new-generation fatty systems

Fats as complex mixtures of acylglycerols with lipid and non-lipid substances are an integral part of human nutrition. The presence of acylglycerols of trans-isomers of fatty acids causes many cardiovascular diseases and metabolic disorders. A promising approach to solving the problem of minimizing the content of these undesirable compounds in food recipes is to create a new generation of fat systems, oleogels, which are the subject of this study. High-oleic sunflower oil was used as a dispersion medium of oleogels, which allows obtaining systems with increased resistance to oxidation, as opposed to the oils of traditional kinds. Sunflower seed wax and tocopherols are chosen as a dispersed phase of these fatty systems. The choice of these components was based on their properties to create a three-dimensional structure in oleogels with specified thermomechanical characteristics. Currently, there is a lack of information on the influence of the content of the dispersed phase on the technological parameters of oleogels, namely oxidative resistance and sorption properties. The purpose of the presented work was to study these features of oleogels and establish their dependences on their composition. To solve this problem, the yield surface method is used in the work. The unknown values of the parameter vector were determined by using regression analysis algorithms. Deviation functionality was minimized by finding the appropriate combinations of the experimental series of predictors. A mathematical model was developed which allows predicting oxidative stability and sorption properties of oleogels based on the data on their composition. The suitable mass fractions of the components of the dispersed phase of oleogels have been determined as follows: tocopherol content is 0.10–0.14 wt.% and the sunflower seed wax content is 1.8–4.0 wt.%. The results obtained can serve as a scientific basis for the development of technology for the industrial production of oleogels as new generation fatty systems.

Effect of Rolling Deformation on Creep Properties of FeCrAl Alloys

FeCrAl alloy is one of the most promising nuclear fuel claddings among many accident tolerant fuel (ATF) materials due to its excellent oxidation resistance and good mechanical properties. However, the effect of process conditions on the creep properties of the FeCrAl alloy is not clear till now. In this study, the impact of a process condition of hot-rolling on the creep properties of FeCrAl alloy was investigated using a nano-indentation creep test under a temperature of 350°C. The microanalysis results indicated that the grain size became smaller with the increase of the hot-rolling thickness reduction. The nano-indentation creep test results showed that the creep power-law stress exponent was about four, and the creep resistance increased when the hot-rolling thickness reduction increased.

Research Progress of First Principles Studies on Oxidation Behaviors of Ti-Al Alloys and Alloying Influence

Ti-Al alloys have good prospects in the aerospace, automobile, and other fields because of their excellent mechanical properties. However, the lack of high temperature oxidation resistance limits their practical applications. Various ways have been used to study their oxidation behaviors. Besides numerous experimental studies focused on the oxidation resistance properties of Ti-Al alloys, theoretical research based on first principles calculations has been carried out on the oxidation mechanisms on the atomic and electronic scales. In recent years, these theoretical studies have provided strong support for understanding the oxidation mechanisms and designing anti-oxidation modification measures. This review will focus on the surface oxidation reactions, element diffusion behaviors and interface bonding properties. The influencing mechanisms of alloying elements on the oxidation properties will be discussed in detail.

Vitis Vinifera Leaf Extract Protects Against Glutamate-Induced Oxidative Toxicity in HT22 Hippocampal Neuronal Cells and Increases Stress Resistance Properties in Caenorhabditis Elegans.

Vitis vinifea has been used for traditional medicines, food, beverages, and dietary antioxidant supplements. The chemical compositions and biological activities of the fruits and seeds have been extensively investigated. However, the biological effects of the leaves are limited, and its anti-neurodegeneration or antiaging activities are little known. The current work aims to study the beneficial effects of V. vinifera leaf extract on neuroprotective effects in HT22 cells, antiaging, and oxidative stress resistance properties in the Caenorhabditis elegans model. The ethanol extract was characterized by phytochemical composition using gas/liquid chromatography–mass spectrometry and reversed-phase high-performance liquid chromatography. The beneficial effects of V. vinifera ethanol (VVE) extract on antioxidant properties, neuroprotective effects, and the underlying mechanisms were studied by in vitro and in vivo studies. In HT22 cells, we found that VVE has a protective effect against glutamate-mediated oxidative stress-induced cell death. The gene expression of cellular antioxidant enzymes such as CAT, SODs, GSTs, and GPx was upregulated by VVE treatment. Moreover, VVE was also shown to alleviate oxidative stress and attenuate reactive oxygen species accumulation in C. elegans. We demonstrated that VVE could upregulate the expression of stress-response genes gst-4 and sod-3 and downregulate the expression of hsp-16.2. Our results suggest that the oxidative stress resistance properties of VVE are possibly involved in DAF-16/FoxO transcription factors. VVE reduced age-related markers (lipofuscin) while did not extend the life span of C. elegans under normal conditions. This study reports the neuroprotective effect and antioxidant activity of V. vinifera leaf extract and suggests its potential as a dietary or alternative supplement to defend against oxidative stress and age-related diseases.

Non-additive sintering of Si2N2O ceramic with enhanced high-temperature strength, oxidation resistance, and dielectric properties

The high-temperature mechanical and dielectric properties of Si2N2O ceramics are often limited by the introduction of a sintering aid. Herein, dense Si2N2O was prepared at 1700 °C by hot-pressing oxidized amorphous Si3N4 powder without sintering additives. A homogeneous network with short-range order and a SiN3O structure was formed in the oxidized amorphous Si3N4 powder during the hot-pressing process. Si2N2O crystals preferentially nucleated at positions within the SiN3O structure and grew into rod-like and plate-like grains. Fully dense ceramics with mainly crystalline Si2N2O and some residual amorphous phases were obtained. The as-prepared Si2N2O possessed a good flexural strength of 311 ± 14.9 MPa at 1400 °C, oxidation resistance at 1500 °C, and a low dielectric loss tangent of less than 5 × 10−3 at 1000 °C.

Properties of Ti(C,N)-based cermets reinforced with ZrO2 whiskers deposited via sulfate flux at high temperatures

Ti(C,N)-based cermets were prepared by vacuum hot-pressing sintering enhanced by the second phase of ZrO2 whiskers via sulfate flux. The effects of ZrO2 whiskers on the material properties of Ti(C,N)-based cermets at high temperature are discussed, including the room temperature microstructure, high-temperature oxidation resistance, and microstructure and mechanical properties at high temperature. The experimental result indicated that the addition of ZrO2 whiskers improves the bending strength, fracture toughness, and oxidation resistance of Ti(C,N)-based cermets at high temperature. At a temperature of 1000 °C, the hardness, flexural strength, fracture toughness and elasticity modulus of the cermets with 7.5 wt% ZrO2 whiskers were 9.32 GPa, 1032 MPa, 6.71 MPa m1/2 and 193.5 GPa, respectively. The high-temperature strength and toughness of Ti(C,N)-based cermets with ZrO2 whiskers were weakened by the softening of grain boundaries, the decrease in elastic modulus, and oxidation. Conversely, the high-temperature strength and toughness of Ti(C,N)-based cermets were increased by maintaining the rod crystal shape of ZrO2 whiskers at a high temperature, enhanced the elastic modulus of cermets through the whiskers, and improved oxidation resistance.

Preparation of Si2N2O wave-transparent and thermal insulation materials with Na2CO3 and BN as aids by pressureless sintering

A hexagonal boron nitride (h-BN)-bonded porous silicon oxynitride (Si2N2O) composite with a low dielectric constant, low thermal diffusivity, and high thermal shock resistance was fabricated by pressureless sintering, and the phase, microstructure, oxidation resistance, and mechanical and dielectric properties of the composites were investigated. The results demonstrated that Na2CO3 facilitated http://www.youdao.com/w/eng/facilitated/javascript:void(0); the generation of Si2N2O. With the subsequent volatilisation of Na2O at high temperatures, near-pure porous Si2N2O ceramics was obtained. However, in the presence of excess Na2CO3 (above 6 wt%), Si2N2O decomposed into Si3N4. The hardness of the Si2N2O/h-BN composite decreased from 1.4 ± 0.15 GPa to 0.4 ± 0.13 GPa with the addition of h-BN, which significantly improved the workability of the material. Moreover, the material exhibited a stable thermal expansion coefficient (3.36 × 10 −6 K−1 at 200 °C and 4.08 × 10 −6 K−1 at 1300 °C), low dielectric constant, and low dielectric loss (ε = 3.26, tan δ = 3.21 × 10−3 at a h-BN content of 9 wt%). Thus, it is a potential wave-transparent and thermal insulation material for microwave sintering furnaces.

Anomalous layer-dependent electronic and piezoelectric properties of 2D GaInS3 nanosheets

Two-dimensional (2D) GaInS3 nanosheets are found to exhibit thermal and structural stabilities, good oxidation resistance, and tunable and layer-dependent electronic properties from first-principles calculations. Remarkably, the nanosheets with arbitrary thickness possess robust in-plane piezoelectricity without the odd-even effect commonly observed in other 2D piezoelectric materials, which is attributed to the retention of noncentrosymmetry resulting from their homogeneous and direct stacking patterns. The piezoelectric stress coefficient e113D of the nanosheets is about 0.23 C/m2, almost independent of the numbers of atomic layers of 2D GaInS3. The stability in piezoelectricity and the high carrier mobility of 2D GaInS3 nanosheets could endow them with promising application prospects in nanoelectronic and nanoelectromechanical devices.

SiC-Coated Carbon Nanotubes with Enhanced Oxidation Resistance and Stable Dielectric Properties.

Carbon nanotubes (CNTs) coated with SiC coating was successfully prepared by pyrolysis of polycarbosilane (PCS) used as a precursor. The function of pyrolysis temperature on the oxidation resistance and the dielectric properties of CNTs/SiC were studied in X-band. The results demonstrate that the obtained dense SiC film can prevent the oxidation of CNTs when the pyrolysis temperature reaches 600 °C. Correspondingly, after heat treatment is at 400 °C for 200 h, the mass loss of P-600 is less than 1.86%, and the real and imaginary parts of the dielectric constant nearly keep constant (ε′ from 14.2 to 14, and ε″ from 5.7 to 5.5). SiC-coated CNTs have a better oxidation resistance than pristine CNTs. Therefore, this work, with a facile preparation process, enhances the oxidation resistance of CNTs at high temperature for a long time and maintains a stable dielectric property, which means CNTs/SiC composites can be good candidates for applications in the field of high-temperature absorbers.

Dual-functional application of Al2O3–B2O3 composite bubble in Al2O3–SiC–C castables as antioxidant and mechanical reinforcement agents

In the present work, the influence of low-cost self-synthesized Al2O3–B2O3 composite bubble on the oxidation resistance and mechanical properties of Al2O3–SiC–C (ASC) castables were investigated. The pre-fabricated composite bubble were characterized in detail. The properties of the ASC castables were measured, including their oxidation indexes, ambient and high-temperature mechanical properties, and microstructural evaluations. The results showed that the introduction of moderate contents of Al2O3–B2O3 composite bubble effectively improved the oxidation resistance and mechanical properties of the ASC castables by volumetric expansion, improved powder filling performance, and the in-situ formation of a high-strength whisker network in the high-temperature flowing liquid phase. These results demonstrated the dual-functional application of Al2O3–B2O3 composite bubble in ASC castables as antioxidants and mechanical reinforcements simultaneously.

Effects of tungsten addition on the microstructural stability and properties of Ti-6.5Al-2Sn-4Hf-2Nb-based high temperature titanium alloys

The microstructural evolution, oxidation resistance and mechanical properties of Ti-6.5Al-2Sn-4Hf-2Nb-based alloys with different contents of tungsten (W) additions ranging from 0 to 4.0 wt.% have been investigated in this study. The addition of W changed the microstructure from Widmanstätten colony of the W-free alloy to basketweave microstructure. After thermal exposure at 650 °C for 1000 h, the retained β phase became less continuous, and secondary β nano-particles with high W concentration were precipitated from α lamellas. Within α lamellas, the W was found to mainly partitioned into the secondary β phase and refined the ordered α2-Ti3Al precipitates due to increased solubility of Nb in α2 phase. High W addition increased activation energy for oxidation, promoting the formation of more uniform and compact compound oxides, therefore substantially enhanced the oxidation resistance of the alloy. Besides, the W addition also improved the room and high-temperature yield strength without obviously losing plasticity after long-time thermal exposure. The improved mechanical performance was mainly attributed to the introduction of more α/β interfaces, the precipitation of secondary β phase and the refined α2 phase with Nb segregation.

Influence of a Discontinuous Process Strategy on Microstructure and Microhardness in Drilling Inconel 718

Nickel-base alloys are proven materials in the fields of the aerospace and oil industry, which is due to their characteristic material properties of high temperature strength, high toughness and good oxidation resistance. These properties are beneficial to applications in technical components in general. However, they also represent challenges for machining. Especially while drilling Inconel 718, high temperatures occur in the chip-formation zone that implicate high thermal load in the material and thus, influence the surface integrity, for example, by causing white layers. Hence, the development of strategies to improve the ability to supply cutting edges with cooling lubricant is becoming increasingly important. In this context, an alternative process design, the discontinuous drilling, takes place, characterized by a periodic interruption of feed motion and thus, chip formation. A minor retraction movement from the contact zone enables the cooling lubricant to reach the cutting edges and to reduce their thermal load. In comparison to the conventional process of drilling Inconel 718, the effects of discontinuous drilling with varying numbers of interruptions on the resulting surface integrity and further parameters of drilling qualities are analyzed. Thereby, the prevention of process-related phase transformations due to thermal impact was discovered when a discontinuous drilling strategy was implemented.

Room-Temperature Coalescence of Tri-n-Octylphosphine-Oxide-Capped Cu-Ag Core-Shell Nanoparticles: Effect of Sintering Agent and/or Reducing Agent

Abstract Metal nanoparticle pastes are useful for nanoinks to form fine conductive patterns in printed electronics. This study reports a novel method for room-temperature coalescence of Cu-Ag core-shell nanoparticles (Cu@Ag NPs), which are expected to have the properties of both migration and oxidation resistance originating from Cu and Ag, respectively. First, oleylamine/oleic-acid capped Cu@Ag NPs were synthesized by the galvanic replacement method. Second, the ligand exchange reaction to tri-n-octylphosphine oxide (TOPO) was carried out on the surface of Cu@Ag NPs. Finally, TOPO-capped Cu@Ag NPs were dipped into methanol containing a sintering agent and/or a reducing agent. When HCl was added as a sintering agent to methanol, the crystallite size of Cu@Ag NPs significantly increased. Furthermore, the almost complete removal of organic compounds and suppression of significant oxidation of Ag and Cu were observed. In consideration of these results, a Cu/Ag conductive thin film was prepared from TOPO-capped Cu@Ag NPs by dipping into methanol containing HCl at room temperature under air atmosphere. Electrical resistivity of the obtained Cu/Ag thin film was (5.1 ± 1.7) × 10−5 Ω m. Microstructural observations and X-ray diffractions of the Cu/Ag thin film revealed that Cu@Ag NPs effectively coalesced at room temperature with slight oxidation.

Oxidation and Corrosion properties of a Novel Al15Ti30Si30Mo15Ni10 High Entropy Alloy fabricated by Spark Plasma Sintering Technology

The need for new advanced high temperature materials is in high demand. High Entropy Alloy (HEAs) has been described to possess excellent mechanical oxidation and good corrosion resistance properties even far above the ambient temperature. Attempts are made in this research to study the corrosion, oxidation, microhardness and densification properties of Al15Ti30Si30Mo15Ni10 HEA produced by spark plasma sintering (SPS) for high temperature applications. In addition, the effects of SPS temperature (800, 900 and 1000°C) on the microstructure and phase formation of the developed HEA were reported. The microstructural modification and phases present were examined using the scanning electron microscope (SEM) equipped with the energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD) respectively. Ordered FCC and BCC systems were identified along with clearly defined crystal lattice along with Mo, Ti and Si rich regions were observed. No pores or cracks were observed from the microstructures. Densification of 98.8% accompanied with microhardness of 1445.29HV was achieved for both HEA at 1000°C. The Al15Ti30Si30Mo15Ni10 HEA fabricated at 1000°C displayed a higher polarization value of 3477 Ω.

Bimodal α-Mo grain structure inducing excellent oxidation resistance in Mo-12Si-8.5B alloy at 1100 °C

Bimodal Mo-12Si-8.5B-1.0wt%ZrB2 alloys were fabricated via hot pressing sintering of a mixture of mechanical alloying Mo-Si-B-ZrB2 powders and unmechanical alloying Mo-Si-B-ZrB2 powders in selected proportion. The bimodal Mo-12Si-8.5B-1.0wt%ZrB2 alloys consisted of fine and coarse α-Mo grains, showing mainly bimodal structure with a part of submicron-scaled α-Mo grains and partial micron-scaled α-Mo grains, where the intermetallics showed weak bimodal distribution but with fine grain structure. Oxidation behavior of the alloys was studied at 1100 °C in air. When average grain sizes of the fine and coarse α-Mo grains in the bimodal alloy were 0.45 μm and 2.15 μm, respectively, and their volume fraction ratio was approximately 1.7:1, a superior oxidation resistant property was achieved. Its mass loss in the transient stage was decreased, showing a 62% decrease compared to that of the ultrafine-grained alloy, and the oxidation recession rate of the alloy substrate was decreased significantly. Additionally, a thinner borosilicate glass scale was formed after oxidation for 30 h which exhibited excellent protective capability. The improved oxidation resistance at 1100 °C was mainly because of the combination of lower oxidation rate of the coarser α-Mo grains and the higher lateral flow rate of the borosilicate glass due to the presence of partial fine α-Mo grains and intermetallics.

Synergistic effects of Al and Ti on the oxidation behaviour and mechanical properties of L12-strengthened FeCoCrNi high-entropy alloys

Synergistic effects of Al and Ti on the oxidation behaviour and mechanical properties of FeCoCrNi high-entropy alloys were systematically investigated. Our results reveal that increasing the Al/Ti ratio slows down the oxidation kinetics at 700−900 °C and changes the oxide scale from TiO2 and spinel oxides to Cr2O3 and Al2O3, leading to a substantial improvement of oxidation resistance. From a mechanical aspect, however, increasing the Al/Ti ratio decreases the mechanical strength, demonstrating a strong trade-off between oxidation resistance and mechanical properties. The underlying mechanisms for the Al and Ti effects on the oxidation resistance and mechanical properties were discussed.

Coating-associated microstructure evolution and elemental interdiffusion behavior at a Mo-rich nickel-based superalloy

Substituting Mo for W in superalloy (SA) design can effectively decrease the alloy density and improve thrust-to-weight ratio of aero engines. However, the outer diffusion of Mo was proved to deteriorate the oxidation resistance and mechanical properties of the coated alloys. In this paper, single phase NiAl alloys (Ni/Al = 50/50 and 60/40, marked as Ni50Al and Ni40Al) and two-phase NiAl alloys (Ni/Al = 70/30, marked as Ni30Al), which always worked as coatings for superalloy, were prepared and employed to form diffusion couples with a Mo-rich superalloy. The average effective interdiffusion coefficients were measured to describe the interdiffusion behavior, and the Ni-30Al/SA diffusion couple showed the lowest average effective interdiffusion coefficients for all elements. Besides, distinct congregation of refractory elements (Mo, Cr, Re, Ta) was observed at the superalloy side in Ni-50Al/SA and Ni-40Al/SA diffusion couples. The different interface phase structure was thought to cause the results, and the initial coating compositions – interface microstructure – elemental interdiffusion behavior relationship was established. This should provide insight into the coat-superalloy interaction and usefully guide designing suitable coats for Mo-rich single crystal superalloy.

Multiscale characterization and representation of variability in ceramic matrix composites

Low density, high strength, and high creep and oxidation resistance properties of ceramic matrix composites (CMCs) make them an ideal choice for use in extreme environments in space and military applications. This paper presents a detailed characterization study of structural and manufacturing flaws in Carbon fiber Silicon-Carbide-Nitride matrix (C/SiNC) CMCs at different length-scales. Energy-dispersive spectroscopy (EDS) is used for the chemical characterization of the material’s elemental constituents. High-resolution multiscale graphs obtained from scanning electron microscope (SEM) and confocal laser scanning microscope (LSM) are used to characterize the distribution and morphology of defects at different length scales. This is followed by the classification and quantification of the common manufacturing defects. An image processing algorithm based on the image segmentation process is developed to quantify the variability of various scale-dependent architectural parameters. Finally, a three-dimensional stochastic representative volume element (SRVE) generation algorithm is developed to provide precise representations of material textures at multiple length scales. The developed algorithm accurately accounts for material features and flaws based on a range of multiscale structural and defects characterization results.

The high-temperature oxidation resistance properties of magnesium alloys alloyed with Gd and Ca

This work studied the high-temperature oxidation resistance properties of Mg alloys with Gd and Ca. The oxidation property of Mg-3.5Gd-xCa (x = 0, 0.5, 1.0 and 3.0 wt%) alloys followed parabolic oxidation kinetics at 500 °C. A stable oxide film was formed on the alloy surface and limited further oxidation. The oxide film was composed of Gd2O3, MgO and MgCO3 for Mg-3.5Gd and was mainly CaO and CaCO3 with increasing Ca content for Mg-3.5Gd-xCa alloys. The high oxidation affinity of Ca caused it to be oxidized preferentially and the fast diffusion of Ca in Mg alloys provided a source for the continuous oxidation of Ca at the surface. The parabolic rate constant, grains size and surface roughness of the oxide film increased with the increasing Ca content in Mg-3.5Gd-xCa alloy. The understanding of multi-element alloying on the oxidation behavior of Mg alloy is helpful for the design of multi-element oxidation-resistant Mg alloys.