Ultra-high Temperature Environments Research Articles

Constructing self-healing ZrSi2-MoSi2 coating for C/C composites with enhanced oxidation protective ability

Cracks are fatal defects of ceramic coatings for carbon/carbon (C/C) composites, through which oxygen will severely destroy the substrate at ultra-high temperature environments. Therefore, the coating materials with rapid self-repairing ability should greatly improve their service stability. Here ZrSi2-MoSi2 coating was designed and fabricated by supersonic plasma spray on SiC coated C/C composites. Results show that it has narrower surface cracks and better self-healing ability at 1450 °C than pure MoSi2 coating. Moreover, it efficiently protects C/C composites from oxidation for 42 h with a mass gain of 1.89% compared to MoSi2 coating with a mass loss of 4.6% for 38 h at 1450 °C. The improvement of the self-healing ability and oxidation protective performance primarily owes to three reasons: 1) the preferential oxidation of ZrSi2 to rapidly form ZrO2/ZrSiO4 particles to reduce the formation of cracks. 2) Low viscosity SiO2 phase to completely heal the cracks. 3) Protective SiO2 layer pinned by ZrO2/ZrSiO4 particles to restrain re-cracking during cooling.

Two-step method to deposit ZrO2 coating on carbon fiber: Preparation, characterization, and performance in SiC composites

Recently, ceramic matrix composites reinforced by short carbon fibers (CFs) attracted increasing attentions. To further improve mechanical properties and oxidation resistances, CFs were subjected to oxidation and acidification followed by sol-gel dip-coating to deposit ZrO2 on their surfaces. ZrO2-Cf/SiC composites were fabricated by joint hot compression molding and sintering, compared to Cf/SiC and SiC prepared by the same method. Microstructural analyses indicated that ZrO2 coatings were successfully deposited on CF surfaces, formed strong bonding and interfaces between CF and the matrix. Meanwhile, CFs were found uniformly distributed in SiC matrix with random orientations. Flexural curves of ZrO2-Cf/SiC and Cf/SiC revealed the presence of “false plasticity” regions after sharp drops, which were quite different from brittle flexural behavior of SiC ceramic. Compression strength of the three samples showed step-up growth. ZrO2-Cf/SiC exhibited the highest value, indicating the introduction of CFs and ZrO2 coatings do have great influence on mechanical performances. After heat treatment, ZrO2-Cf/SiC exhibited better oxidation resistance than Cf/SiC, with weight loss ratios estimated to − 3.76% and − 6.43%, respectively. These improved properties indicated that ZrO2-Cf/SiC would be excellent alternatives to other existence materials under ultra-high temperature environments.

Pressureless densification, microstructure tailoring and properties of Ta0.8Hf0.2C-based composites

Ta0.8Hf0.2C (TH) ceramics are desirable for applications in ultra-high temperature environments, but they are difficult to be sintered pressurelessly. TH ceramics were densified up to 98.8% from commercial powders via pressureless sintering (PLS) at 2473K. SiC was introduced as secondary phase to tailor microstructures and improve properties of TH. The influence of SiC volume fraction on the densification, microstructure evolution and room-temperature properties of TH-based ceramics were examined. Average grain size of TH was refined from 13.6 down to 2.0μm. 10vol% SiC addition contributed to densification of Ta0.8Hf0.2C-SiC (THS) composites with a relative density of 99.6%. The mechanical properties of THS were fairly good, and thermal properties of sintered THS displayed a remarkable improvement compared with TH: the coefficient of thermal expansion (CTE) showed a reduction of 8.6% while the thermal conductivity increased from 18.6 to 41.5W/mK.

Transformations to granular zircon revealed: Twinning, reidite, and ZrO2 in shocked zircon from Meteor Crater (Arizona, USA)

Abstract Granular zircon in impact environments has long been recognized but remains poorly understood due to lack of experimental data to identify mechanisms involved in its genesis. Meteor Crater in Arizona (USA) contains abundant evidence of shock metamorphism, including shocked quartz, the high-pressure polymorphs coesite and stishovite, diaplectic SiO2 glass, and lechatelierite (fused SiO2). Here we report the presence of granular zircon, a new shocked-mineral discovery at Meteor Crater, that preserve critical orientation evidence of specific transformations that occurred during formation at extreme impact conditions. The zircon grains occur as aggregates of sub-micrometer neoblasts in highly shocked Coconino Sandstone (CS) comprised of lechatelierite. Electron backscatter diffraction shows that each grain consists of multiple domains, some with boundaries disoriented by 65° around <110>, a known {112} shock-twin orientation. Other domains have {001} in alignment with {110} of neighboring domains, consistent with the former presence of the high-pressure ZrSiO4 polymorph reidite. Additionally, nearly all zircon preserve ZrO2 + SiO2, providing evidence of partial dissociation. The genesis of CS granular zircon started with detrital zircon that experienced shock twinning and reidite formation at pressures from 20 to 30 GPa, ultimately yielding a phase that retained crystallographic memory; this phase subsequently recrystallized to systematically oriented zircon neoblasts, and in some areas partially dissociated to ZrO2. The lechatelierite matrix, experimentally constrained to form at >2000 °C, provided the ultrahigh-temperature environment for zircon dissociation (∼1670 °C) and neoblast formation. The capacity of granular zircon to preserve a cumulative pressure-temperature record has not been recognized previously, and provides a new method for investigating histories of impact-related mineral transformations in the crust at conditions far beyond those at which most rocks melt.

Development of a multi-variate calibration approach for quantitative analysis of oxidation resistant Mo–Si–B coatings using laser ablation inductively coupled plasma mass spectrometry

Nowadays, for the production of oxidation protection coatings in ultrahigh temperature environments, alloys of Mo–Si–B are employed. The properties of the material, mainly the oxidation resistance, are strongly influenced by the Si to B ratio; thus reliable analytical methods are needed to assure exact determination of the material composition for the respective applications.For analysis of such coatings, laser ablation inductively coupled mass spectrometry (LA-ICP-MS) has been reported as a versatile method with no specific requirements on the nature of the sample. However, matrix effects represent the main limitation of laser-based solid sampling techniques and usually the use of matrix-matched standards for quantitative analysis is required. In this work, LA-ICP-MS analysis of samples with known composition and varying Mo, Si and B content was carried out. Between known analyte concentrations and derived LA-ICP-MS signal intensities no linear correlation could be found. In order to allow quantitative analysis independent of matrix effects, a multiple linear regression model was developed. Besides the three target analytes also the signals of possible argides (40Ar36Ar and 98Mo40Ar) as well as detected impurities of the Mo–Si–B coatings (108Pd) were considered. Applicability of the model to unknown samples was confirmed using external validation. Relative deviations from the values determined using conventional liquid analysis after sample digestion between 5 and 10% for the main components Mo and Si were observed.

Hafnium carbide protective layer coatings on carbon/carbon composites deposited with a vacuum plasma spray coating method

A pure hafnium-carbide (HfC) coating layer was deposited onto carbon/carbon (C.C) composites using a vacuum plasma spray system (VPS). By introducing a SiC buffer layer, we successfully integrated C.C composites with a 110-μm-thick protective coating layer of HfC. Compared to the conventional chemical vapor deposition process, the HfC coating process by VPS showed increments in the growth rate, thickness, and hardness. The growth behavior and morphology of HfC coatings were investigated by FE-SEM, EDX, and XRD. In addition, the thermal ablation test results showed that the HfC coating layer perfectly protected the C.C layer from thermal ablation and oxidation. Consequently, we expect that this ultra-high temperature ceramic coating method, and the subsequent microstructure that it creates, can be widely applied to improve the thermal shock and oxidation resistance of materials under ultra-high temperature environments.

Preparation and characterization of highly porous Yb2SiO5 ceramics using water-based freeze-casting

This study introduces a new, highly porous Yb2SiO5 ceramic prepared using a water-based freeze-casting technique. The prepared porous Yb2SiO5 ceramic had ultra-high porosity (82–86 %) and tailored pore structures. The effects of sintering temperature on the pore structure, thermal conductivity, and mechanical properties of these ceramics were investigated. The sample with 15 vol% solid content prepared at 1450 °C had ultra-low linear shrinkage (4.85 %), ultra-high porosity (83.95 %), high compressive strength (2.15 MPa), and low thermal conductivity (0.121 W/m K). In addition, this sample showed a relatively high compressive strength (1.15 MPa) at 1500 °C. These results highlight the potential application of highly porous Yb2SiO5 ceramics as thermal insulator materials in ultra-high temperature environments.

In-Fiber Gratings for Simultaneous Monitoring Temperature and Strain in Ultrahigh Temperature

In this letter, a pair of regenerated gratings with Bragg wavelengths of 1547 and 1304 nm in a single piece of single-mode fiber has been fabricated for simultaneous monitoring of temperature and strain in ultrahigh temperature environment. A $3\times 3$ matrix is used to characterize the cross sensitivity of the proposed sensor in which the strain sensitivity varies with temperature change. The proposed structure exhibits the deviation of 28.3 $\mu \varepsilon $ and 4.1 °C at the ranges of 0–1000 $\mu \varepsilon $ and 25 °C–900 °C, respectively.

High to ultrahigh temperature contact metamorphism and dry partial melting of the Tasiuyak paragneiss, Northern Labrador

AbstractContact aureoles of the anorthositic to granitic plutons of the Mesoproterozoic Nain Plutonic Suite (NPS), Labrador, are particularly well developed in the Palaeoproterozoic granulite facies, metasedimentary, Tasiuyak gneiss. Granulite facies regional metamorphism (MR),c. 1860 Ma, led to biotite dehydration melting of the paragneiss and melt migration, leaving behind biotite‐poor, garnet–sillimanite‐bearing quartzofeldspathic rocks. Subsequently, Tasiuyak gneiss within ac. 1320 Ma contact aureole of theNPSwas statically subjected to lower pressure, but higher temperature conditions (MC), leading to a second partial melting event, and the generation of complex mineral assemblages and microstructures, which were controlled to a large extent by the textures of theMRassemblage. This control is clearly seen in scanning electron microscopic images of thin sections and is further supported by phase equilibria modelling. Samples collected within the contact aureole near Anaktalik Brook, west of Nain, Labrador, mainly consist of spinel–cordierite and orthopyroxene–cordierite (or plagioclase) pseudomorphs afterMRsillimanite and garnet, respectively, within a quartzofeldspathic matrix. In addition, some samples contain fine‐grained intergrowths of K‐feldspar–quartz–cordierite–orthopyroxene inferred to be pseudomorphs after osumulite. Microstructural evidence of the former melt includes (i) coarse‐grained K‐feldspar–quartz–cordierite–orthopyroxene domains that locally cut the rock fabric and are inferred to represent neosome; (ii) very fine‐ to medium‐grained cordierite–quartz intergrowths interpreted to have formed by a reaction involving dissolution of biotite and feldspar in melt; and (iii) fine‐scale interstitial pools or micro‐cracks filled by feldspar interpreted to have crystallized from melt. Ultrahigh temperature (UHT) conditions during contact metamorphism are supported by (i) solidus temperatures >900 °C estimated for all samples, coupled with extensive textural evidence for contact‐related partial melting; (ii) the inferred (former) presence of osumilite; and (iii) titanium‐in‐quartz thermometry indicating temperatures within error of 900 °C. TheUHTenvironment in which these unusual textures and minerals were developed was likely a consequence of the superposition of more than one contact metamorphic event upon the already relatively anhydrous Tasiuyak gneiss.

Ultra-high temperature oxidation of a hafnium carbide-based solid solution ceramic composite

Hafnium carbide-based solid solution ceramics with yttria additions were consolidated via hot pressing utilizing chromium carbide as a transient liquid sintering agent. Selected samples were oxidized at temperatures exceeding 2200°C under high velocity airflow to determine their potential for service in ultra-high temperature environments. Cross-sectional examination revealed a complex multi-layer scale comprising a highly porous exterior region, a dense multi-phase interior region, and an oxygen- and carbon-containing interlayer consisting of nanocrystalline graphite in an amorphous or nanocrystalline oxide matrix. Outward diffusion of mobile cations is speculated to play an important role in establishing the observed scale morphology.

Development of non-eroding rocket nozzle throat for ultra-high temperature environment

The powder processing methods including powder metallurgy (P/M) and powder injection molding (PIM) techniques for tungsten (W)–rhenium (Re) were employed to produce a W–Re rocket nozzle. The composition of W–Re was determined by 25wt.% of Re to avoid the formatting brittle sigma (σ) phase. The samples for analysis of the densification behavior on sintering were prepared by die pressing and cold isostatic pressing (CIP). The feedstock for the PIM process was produced by mixing the W–25wt.% Re powder and binder system based on a wax-polymer with an optimum solid loading through the twin-extruder mixer. The injection molded specimens were debound to extract and decompose the binders via the solvent and thermal debindings. The debound samples were sintered in a hydrogen atmosphere. After sintering, hot isostatic pressing (HIP) was carried out in an argon atmosphere to enhance the density.The dilatometry experiments were performed to analyze and predict a densification behavior during sintering. The master sintering curve (MSC) model was used to characterize the densification behavior with a minimal set of preliminary experiments. The mechanical properties were evaluated through microstructure and chemical composition measured by EDX–SEM and X-ray diffraction (XRD).Finally, the eroding test was conducted using the W–25wt.% Re rocket nozzle produced by PIM under the high temperature. After carrying out erosion tests, the erosion rate, hardness and microstructure were evaluated.

A reactive force-field for Zirconium and Hafnium Di-Boride

Zirconium and Hafnium Di-Boride are the two major material systems that are of critical importance for applications in ultra-high temperature environments where both oxidation and mechanical damage mechanisms (such as creep) are operative. Atomistic simulations of these materials at finite temperatures have been hampered due to the unavailability of inter-atomic potentials for the involved elements. In this paper, we present the development of interatomic potentials for both ZrB2 and HfB2 within the ReaxFF framework—thus enabling modeling of chemical reactions. The parameters of the reactive force field are derived by fitting to detailed quantum mechanical simulations of ZrB2 and HfB2 clusters and crystal structures.

Microstructural characterization of non-equilibrated 4D carbon/carbon composites in ultrahigh temperature environment

A comparative study has been carried out on microstructure, ultrahigh temperature tensile properties, and erosion behavior of non-equilibrated four-directional reinforced carbon/carbon composites, prepared using polyacrylonitrile based carbon fibers as the reinforcement and coal-tar pitch as the matrix, to assess the effect of microstructural changes on the properties of the composites in an ultrahigh temperature environment. X-ray diffraction and scanning electron microscopic analyses suggest that the carbon matrix is highly graphitized, which is composed of mosaic and domain structures. The composites retain superior tensile properties with a visco-plastic behavior at ultrahigh temperature, which is consistent with the observation of mixed microstructural changes, crack propagation, and deflection as well as fiber debonding. The ablation behavior of non-equilibrated four-directional reinforced carbon/carbon composites is mainly dominated by thermo-chemical ablation and mechanical erosion, and different microstructures exhibit distinguished erosion mechanisms.

Investigation of a novel bayonet tube high temperature heat exchanger with inner and outer fins

In this paper, a novel bayonet tube high temperature heat exchanger (HTHE) with inner and outer fins is presented. It can be used in the ultra high temperature environment, such as hydrogen production, very high temperature reactor and externally fired combined cycle. Numerical investigation of heat transfer performance on the inside of bayonet element has been conducted for structure design. The numerical results suggest that the inner fin and inner tube should not be welded together. It is recommended that the air enters from the inner tube and exits from the annular space in the high temperature zone. A high temperature experimental system has been established to test the heat transfer and pressure drop characteristics of the HTHE. The surface area density of the tested HTHE is 6 times higher than that of the bare bayonet tube heat exchanger. The experimental results indicate that the mass flow rate on both sides and inlet temperature on the fuel gas side have a significant effect on the heat transfer rate and effectiveness, while the pressure drop ratios are mainly affected by the mass flow rate rather than the inlet temperature. Comparison between the tested HTHE and the similar HTHE without fins indicates that the proposed HTHE has a significant potential to improve the comprehensive heat transfer performance.

ZrB2-SiC 세라믹스의 미세구조와 기계적 물성에 미치는 B4C 첨가효과

ZrB₂ has a melting point of 3245℃ and a relatively low density of 6.1 g/㎤, which makes this a candidate for application to ultrahigh temperature environments over 2000℃. Beside these properties, ZrB₂ is known to have excellent resistance to thermal shock and oxidation compared with other non-oxide engineering ceramics. In order to enhance such oxidation resistance, SiC was frequently added to ZrB₂?based systems. Due to nonsinterability of ZrB₂?based ceramics, research on the sintering aids such as B₄C or MoSi₂ becomes popular recently. In this study, densification and high-temperature properties of ZrB₂-SiC ceramics especially with B₄C are investigated. ZrB₂-20 vol% SiC system was selected as a basic composition and B₄C or C was added to this system in some extents. Mixed powders were sintered using hot pressing (HP). With sintered bodies, densification behavior and high-temperature (up to 1400℃) properties such as flexural strength, hardness, and so on were examined.

Design and Fabrication of a Piezoresistive Pressure Sensor for Ultra High Temperature Environment

In order to solve the pressure measurement problem in the harsh environment, a piezoresistive pressure sensor has been developed, which can be used under high temperature above 200°C and is able to endure instantaneous ultra high temperature (2000°C, duration≦2s) impact. Based on the MEMS (Micro Electro-Mechanical System) and integrated circuit technology, the piezoresistive pressure sensor's sensitive element was fabricated and constituted by silicon substrate, a thin buried silicon dioxide layer, four p-type resistors in the measuring circuit layer by boron ion implantation and photolithography, the top SiO2 layer by oxidation, stress matching Si3N4 layer, and a Ti-Pt-Au beam lead layer for connecting p-type resistors by sputtering. In order to decrease the leak-current influence to sensor in high temperature above 200°C, the buried SiO2 layer with the thickness 367 nm was fabricated by the SIMOX (Separation by Implantation of Oxygen) technology, which was instead of p-n junction to isolate the upper measuring circuit layer from Si substrate. In order to endure instantaneous ultra high temperature impact, the mechanical structure with cantilever & diaphragm and transmitting beam was designed. By laser welding and high temperature packaging technology, the high temperature piezoresistive pressure sensor was fabricated with range of 120MPa. After the thermal compensation, the sensor's thermal zero drift k0 and thermal sensitivity drift ks were easy to be less than 3×10−4FS/°C. The experimental results show that the developed piezoresistive pressure sensor has good performances under high temperature and is able to endure instantaneous ultra high temperature impact, which meets the requirements of modern industry, such as aviation, oil, engine, etc.

Estimation of Steady-State Creep Behavior of Al2O3/YAG Eutectic Composite by Image-Based Finite Element Analysis

Al 2 O 3 / YAG eutectic composite has been developed for a structural material used in ultra high temperature environments over 1500°C such as a gasturbine. Creep behavior is one of the important material properties in ultra high temperature materials. In the present study, we propose an image-based finite element analysis for estimating the steady state creep behavior of the Al2O3/YAG eutectic composite. In the image-based finite element analysis, microstructure of the material taken by a SEM is modeled into a finite element mesh using a software for image process. Then finite element creep analyses are carried out to obtain the steady state creep behavior of the Al2O3/YAG eutectic composite by using steady state creep constitutive equations for both Al2O3 single crystal and YAG single crystal. The results of steady state creep behavior obtained from the image-based finite element analysis are compared with the experimental results. It is found that the steady state creep behavior of the Al2O3/YAG eutectic composite is accurately estimated by the image-based finite element analysis. Furthermore, we examine the effect of volume fractions of the constituents on the steady state creep behavior of the Al2O3/YAG eutectic composite.

Processing and characterization of silicon carbon-nitride ceramics: application of electrical properties towards MEMS thermal actuators

Abstract This paper reports the development of electrically conductive silicon carbon-nitride (SiCN) for harsh-environment MEMS applications. SiCN is a new class of polymer-derived bulk ceramics for ultra-high temperature and corrosive environment applications; however, as-pyrolyzed SiCN is electrically insulating. Through post-pyrolysis annealing at 1400 °C in a hot isostatic press in a nitrogen atmosphere poly(urea-methyl-vinyl)silazane-derived SiCN MEMS devices were fabricated that exhibit a room temperature electrical resistivity of 2–5.5 Ω cm. The material was examined using linear four-probe, X-ray diffraction, Fourier transform infrared spectroscopy and SEM. This integrated materials/micromachining process enables the realization of a new class of (electro-thermo-mechanical) devices not previously possible in SiCN, and thus takes polymer-derived ceramic (PDC) microsystems technology to the next level of complexity. SiCN lateral thermal actuators and micro-grippers for moving chip-sized objects were fabricated to demonstrate an application of this functionalized material. This work is the first to demonstrate electro-thermo-mechanical transducers fabricated from polymer-derived SiCN.

イメージベース有限要素法によるＡｌ２Ｏ３／ＹＡＧ共晶複合材料の定常クリープ特性の推算

Al2O3/YAG eutectic composite has been developed for a structural material used in ultra high temperature environments more than 1500°C such as in a gas turbine. Creep behavior is one of the important material properties in ultra high temperature materials. In the present study, we propose image-based finite element analysis for estimating the steady state creep behavior of the Al2O3/YAG eutectic composite. In the image-based finite element analysis, micro-structure of the material taken by a SEM is modeled into a finite element mesh using a software for image processing. Then finite element creep analysis is carried out to obtain the steady state creep behavior of the Al2O3/YAG eutectic composite by using steady state creep constitutive equations for both Al2O3 single crystal and YAG single crystal. The results of steady state creep behavior obtained from the image-based finite element analysis are compared with the experimental results. It is found that the steady state creep behavior of the Al2O3/YAG eutectic composite is accurately estimated by the image-based finite element analysis. Furthermore, we examine the effect of volume fractions of the constituents on the steady state creep behavior of the Al2O3/YAG eutectic composite.

Development of a new ULT Scanning Tunneling Microscope at University of Tokyo

We describe design concepts and some technical details of a new ultra-low temperature scanning tunneling microscope (ULT-STM) which is now under construction at University of Tokyo. It is designed to work with an atomic resolution at temperatures down to 20 mK and in magnetic fields up to 6 T. It is possible to change samples and STM tips keeping ultra high vacuum and low temperature environments, which allows us to study almost all conducting materials and adsorbed samples.