Sandwich probe temperature sensor based on In_(2)O_(3)-IZO thin film for ultra-high temperatures

High-temperature thin-film thermocouples(TFTCs)have attracted significant attention in the aerospace and steel metallurgy industry.However,previous studies on TFTCs have primarily focused on the two-dimensional planar-type,whose thermal sensitive area has to be perpendicular to the test environment,and therefore affects the thermal fluids pattern or loses accuracy.In order to address this problem,recent studies have developed three-dimensional probe-type TFTCs,which can be set parallel to the test environment.Nevertheless,the probe-type TFTCs are limited by their measurement threshold and poor stability at high temperatures.To address these issues,in this study,we propose a novel probe-type TFTC with a sandwich structure.The sensitive layer is compounded with indium oxide doped zinc oxide and fabricated using screen-printing technology.With the protection of sandwich structure on electrode film,the sensor demonstrates robust high-temperature stability,enabling continuous working at 1200℃ above 5 h with a low drift rate of 2.3℃·h^(−1).This sensor exhibits a high repeatability of 99.3% when measuring a wide range of temperatures,which is beyond the most existing probe-type TFTCs reported in the literature.With its excellent high-temperature performance,this temperature sensor holds immense potentials for enhancing equipment safety in the aerospace engineering and ensuring product quality in the steel metallurgy industry.

DIRECTIONALLY SOLIDIFIED MICROSTRUCTURE OF AN ULTRA-HIGH TEMPERATURE Nb-Si-Ti-Hf-Cr-Al ALLOY

The directionally solidified samples of an ultra-high temperature Nb-Si-Ti-Hf-Cr-Al alloy have been prepared with the use of an electron beam floating zone melting (EBFZM) furnace, and their microstructural characteristics have been analyzed. All the primary dendrites of Nb solid solution (Nbss), eutectic colonies of Nba, plus (Nb, Ti)3 Si/(Nb, Ti)5 Si3 and chains of (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates align along the growth direction of the samples. With increasing of the withdrawing rate, the microstructure is refined, and the amounts of Nbss+ (Nb, Ti)3 Si/(Nb, Ti)5 Si3 eutectic colonies and (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates increase. There appear nodes in the (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates.

The temperature-dependent fracture strength model for ultra-high temperature ceramics

Breaking down the entire structure of a material implies severing all the bonds between its atoms either by applying work or by heat transfer. Because bond-breaking is indifferent to either means, there is a kind of equivalence between heat energy and strain energy. Based on this equivalence, we assume the existence of a constant maximum storage of energy that includes both the strain energy and the corresponding equivalent heat energy. A temperaturedependent fracture strength model is then developed for ultrahigh temperature ceramics （UHTCs）. Model predictions for UHTCs, HfB2, TiC and ZrB2, are presented and compared with the experimental results. These predictions are found to be largely consistent with experimental results.

Fabrication and Thermal Structural Characteristics of Ultra-high Temperature Ceramic Struts in Scramjets

ZrB_2-SiC based ultra-high temperature ceramic（UHTC） struts were firstly proposed and fabricated with the potential application in the combustor of scramjets for fuel injection and flame-holding for their machinability and excellent oxidation/ablation resistance in the extreme harsh environment. The struts were machined with electrospark wire-electrode cutting techniques to form UHTC into the desired shape, and with laser drilling to drill tiny holes providing the channels for fuel injection. The integrated thermal-structural characteristic of the struts was evaluated in high-temperature combustion environment by the propane-oxygen free jet facility, subject to the heat flux of 1.5 MW/m^2 lasting for 300 seconds, and the struts maintained integrity during and after the first experiment. The experiments were repeated for verifying the reusability of the struts. Fracture occurred during the second repeated experiment with the crack propagating through the hole. Finite element analysis（FEA） was carried out to study the thermal stress distribution in the UHTC strut. The simulation results show a high thermal stress concentration occurs at the hole which is the crack initiation position. The phenomenon is in good agreement with the experimental results. The study shows that the thermal stress concentration is a practical key issue in the applications of the reusable UHTC strut for fuel injection structure in scramjets.

Effects of mechanical boundary conditions on thermal shock resistance of ultra-high temperature ceramics

The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance（TSR） of ultra-high temperature ceramics（UHTCs） are studied by investigating the TSR of a UHTC plate with various types of constraints under the first, second, and third type of thermal boundary conditions. The TSR of UHTCs is strongly dependent on the heat transfer modes and severity of the thermal environments. Constraining the displacement of the lower surface in the thickness direction can significantly decrease the TSR of the UHTC plate, which is subject to the thermal shock at the upper surface. In contrast, the TSR of the UHTC plate with simply supported edges or clamped edges around the lower surface is much better.

Rapid Directional Solidification with Ultra-High Temperature Gradient and Cellular Spacing Selection of Cu-Mn Alloy

The detailed laser surface remelting experiments of Cu-31.4 wt pct Mn and Cu-26.6 wt pct Mn alloys on a 5 kW CO2 laser were carried out to study the effects of processing parameters (scanning velocity, output power of laser) on the growth direction of microstructure in the molten pool and cellular spacing selection under the condition of ultra-high temperature gradient and rapid directional solidification. The experimental results show that the growth direction of microstructure is strongly affected by laser processing parameters. The ultra-high temperature gradient directional solidification can be realized on the surface of samples during laser surface remelting by controlling laser processing parameters, the temperature gradient and growth velocity can reach 106 K/m and 24.1 mm/s, respectively, and the solidification microstructure in the center of the molten pool grows along the laser beam scanning direction. There exists a distribution range of cellular spacings under the laser rapid solidification conditions, and the average spacing decreases with increasing of growth rate. The maximum, λmax, minimum, λmin, and average primary spacing, A, as functions of growth rate, Vb, can be given by,λmax=12.54Vb-0.61, λmin=4.47 Vb-0.52, λ=9.09Vb-0.62, respectively. The experimental results are compared with the current Hunt-Lu model for rapid cellular/dendritic growth, and a good agreement is found.

Porous Ultra-high Temperature Ceramics for Ultra-high Temperature Thermal Protection System

Ultra-high temperature ceramics(UHTCs)are a family of borides,carbides and nitrides of transition elements such as hafnium,zirconium,tantalum and niobium.They exhibit the highest known melting points,good mechanical strength,good chemical and thermal stability under certain conditions.In last decade,researchers dedicated to characterize porous UHTCs aiming to develop novel thermal insulating materials that could withstand temperatures over 2000℃.In this article,the preparation and characteristics of porous UHTCs were reviewed.Dry processing,colloidal processing and solution processing routes have been used to prepare porous UHTCs with porosities ranging from 5%to 97%and pore sizes ranging from hundreds of nanometers to hundreds of micrometers.The obtained porous UHTCs are chemically and dimensionally stable at temperatures up to 2000℃ during static state high-temperature thermal aging.

Ultra-high Temperature Ceramic Coatings:A Review on Preparation Technology and Development Prospect

Ultra-high temperature ceramic coatings have ultra-high melting points,excellent mechanical properties and high temperature ablation resistance.These unique performance combinations turn it into a promising material for use in extreme environment structures in rockets and hypersonic vehicles,particularly nozzles,leading edges and engine components.In this paper,various preparation methods of ultra-high temperature ceramic coatings were reviewed,including plasma spraying,chemical vapor deposition,pack cementation,slurry sintering,hot pressing and their research progress.Meanwhile,some new preparation methods of high temperature coatings,such as ion beam deposition,ultrasonic spraying,metal organic frame work coating,and magnetron sputtering,were introduced.The development trend of ultra-high temperature coatings was prospected as well.

“Low Creep Ultra-high Temperature Corundum Mullite Kiln Furnature” Developed by Sinosteel LIRR Rewarded as “National New Product”

Recently, ＂ Low Creep Ultra-high Temperature Corundum Mullite Kiln Fumature＂ developed by Sinosteel L1RR was listed in The National New Product Program in 2012 of The Ministry of Science and Technology of China.

Ultra-High Temperature Gratings

Regenerated gratings seeded by type-I gratings are shown to withstand temperatures beyond 1000 ℃. The method of regeneration offers a new approach to increasing temperature resistance of stable fibre Bragg and other gratings. These ultra-high temperature （UHT） gratings extend the applicability of silicate based components to high temperature applications such as monitoring of smelters and vehicle and aircraft engines to high power fibre lasers.

Solidification Microstructures of a Single-crystal Superalloy under Ultra-high Temperature Gradient Conditions

The solidification microstructures and solute segregation of a newly developed hot corrosion resistant single-crystal Ni-base superalloy were investigated with a zone-melting and ultra-high thermal gradient unidirectional solidification apparatus.Compared with the microstructures solidified at conventional low thermal gradient conditions,the dendrite arm spacings,the interdendritic microporosity and γ/γ' eutectic,and the severity of solute segregation of the single-crystal superalloy solidified at ultra-high thermal gradient conditions were considerably reduced.It was shown that the microstructure solidified under ultra-high thermal gradient condition is ideal for the full exploitation of the excellent property potentials of single-crystal superalloys.

Application of phase diagram calculations to development of new ultra-high temperature structural materials

In-situ refractory metal intermetallic composites(RMICs) based either on (Nb, Si) or (Mo, Si, B) are candidate materials for ultra-high temperature applications (>1400 ℃). To provide a balance of mechanical and environmental properties, Nb-Si composites are typically alloyed with Ti and Cr, and Mo-Si-B composites are alloyed with Ti. Phase diagrams of Nb-Cr-Ti-Si and Mo-Si-B-Ti, as prerequisite knowledge for advanced materials design and processing development, are critically needed. The phase diagrams in the metal-rich regions of multicomponent Nb-Cr-Ti-Si and Mo-Si-B-Ti were rapidly established using the Calphad (Calculation of phase diagram) approach coupled with key experiments. The calculated isotherms, isopleths, and solidification paths were validated by experimental work. The important heterogeneous multiphase equilibria in both quaternary systems identified will offer engineers the opportunity to develop materials with a balance of properties for high-temperature applications.

High speed laser cladding as a new approach to prepare ultra-high temperature ceramic coatings

Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.

Emergent ultra-high temperature ferromagnetism in La_(2)CoO_(4±x) thin films

Searching for novel ferromagnetic oxides with high Curie temperature(TC)has been one of the main goals for oxide spintronics.The well-known perovskite cobaltate LaCoO_(3) is a classical ferromagnet in its thin-film form;however,it suffers from a low TC(~85 K).Here we report a new type of ferromagnetic La-Co-O films with an ultrahigh TC of~820 K.They are fabricated by pulsed laser deposition from a LaCoO_(3) target at low oxygen partial pressures.Detailed structural analysis indicates that they crystallize in terms of the Ruddlesden–Popper phase of La_(2)CoO_(4±x).In sharp contrast to the antiferromagnetism of bulk La_(2)CoO_(4),the strong ferromagnetism in the La_(2)CoO_(4±x) thin films is firmly demonstrated by magnetometry measurements,X-ray magnetic circular dichroism characterization,and magnetotransport experiments.More importantly,density functional theory calculations indicate that the nonstoichiometric oxygen induces an antiferromagnetic-to-ferromagnetic phase transition,accompanied by the orbital reconstruction of Co 3d electrons.Thus,our study provides an attractive strategy for designing or synthesizing exotic magnetic oxides with high ordering temperatures.

Effects of the extrusion parameters on microstructure,texture and room temperature mechanical properties of extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy

Microstructure,texture,and mechanical properties of the extruded Mg-2.49Nd-1.82Gd-0.2Zn-0.2Zr alloy were investigated at different extrusion temperatures(260 and 320℃),extrusion ratios(10:1,15:1,and 30:1),and extrusion speeds(3 and 6 mm/s).The experimental results exhibited that the grain sizes after extrusion were much finer than that of the homogenized alloy,and the second phase showed streamline distribution along the extrusion direction(ED).With extrusion temperature increased from 260 to 320℃,the microstructure,texture,and mechanical properties of alloys changed slightly.The dynamic recrystallization(DRX)degree and grain sizes enhanced as the extrusion ratio increased from 10:1 to 30:1,and the strength gradually decreased but elongation(EL)increased.With the extrusion speed increased from 3 to 6 mm/s,the grain sizes and DRX degree increased significantly,and the samples presented the typical<2111>-<1123>rare-earth(RE)textures.The alloy extruded at 260℃ with extrusion ratio of 10:1 and extrusion speed of 3 mm/s showed the tensile yield strength(TYS)of 213 MPa and EL of 30.6%.After quantitatively analyzing the contribution of strengthening mechanisms,it was found that the grain boundary strengthening and dislocation strengthening played major roles among strengthening contributions.These results provide some guidelines for enlarging the industrial application of extruded Mg-RE alloy.

Advances in ultra-high temperature ceramics,composites,and coatings

Ultra-high temperature ceramics(UHTCs)are generally referred to the carbides,nitrides,and borides of the transition metals,with the Group IVB compounds(Zr&Hf)and TaC as the main focus.The UHTCs are endowed with ultra-high melting points,excellent mechanical properties,and ablation resistance at elevated temperatures.These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles,particularly nozzles,leading edges,and engine components,etc.In addition to bulk UHTCs,UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics.Recently,high-entropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials.This review presents the state of the art of processing approaches,microstructure design and properties of UHTCs from bulk materials to composites and coatings,as well as the future directions.

Design, Preparation and Properties of Carbon Fiber Reinforced Ultra-High Temperature Ceramic Composites for Aerospace Applications： A Review

Carbon fiber reinforced ultra-high temperature ceramic （UHTC） composites, consisting of carbon fibers embedded in a UHTC-matrix or a C-SiC-UHTC-matrix, are deemed as the most viable class of materials that can overcome the poor fracture toughness and thermal shock resistance of monolithic UHTC ma- terials, and also improve the oxidation resistance and ablation resistance of C/C and C/SiC composites at ultra-high temperatures. In this review, we summarize the different processing routes of the compos- ites based on the UHTC introducing methods, including chemical vapor infiltration/deposition （CVI/D）, precursor infiltration and pyrolysis （PIP）, reactive melt infiltration （RMI）, slurry infiltration （SI）. in-sito reaction, hot pressing （HP）, etc; and the advantages and drawbacks of each method are briefly dis- cussed. The carbon fiber reinforced UHTC composites can be highly tailorable materials in terms of fiber. interface, and matrix. From the perspective of service environmental applications for engine propul- sions anti hypersonic vehicles, the material designs （mainly focusing on the composition, quantity, structure of matrix, as well as the architecture of carbon fibers, UHTCs and pores）, their relevant processing routes and properties （emphasizing on the mechanical and ablation properties） are discussed in this paper. In addition, we propose a material architecture to realize the multi-function through changing the distri- bution of carbon fibers, UHTCs and pores, which will be an important issue for future development of carbon fiber reinforced UHTC composites.

Elucidating the role of preferential oxidation during ablation:Insights on the design and optimization of multicomponent ultra-high temperature ceramics

Multicomponent ultra-high temperature ceramics(UHTCs)are promising candidates for thermal protection materials(TPMs)used in aerospace field.However,finding out desirable compositions from an enormous number of possible compositions remains challenging.Here,through elucidating the role of preferential oxidation in ablation behavior of multicomponent UHTCs via the thermodynamic analysis and experimental verification,the correlation between the composition and ablation performance of multicomponent UHTCs was revealed from the aspect of thermodynamics.We found that the metal components in UHTCs can be thermodynamically divided into preferentially oxidized component(denoted as MP),which builds up a skeleton in oxide layer,and laggingly oxidized component(denoted as ML),which fills the oxide skeleton.Meanwhile,a thermodynamically driven gradient in the concentration of MP and ML forms in the oxide layer.Based on these findings,a strategy for pre-evaluating the ablation performance of multicomponent UHTCs was developed,which provides a preliminary basis for the composition design of multicomponent UHTCs.

Sol–gel derived porous ultra-high temperature ceramics

Ultra-high temperature ceramics(UHTCs)are considered as a family of nonmetallic and inorganic materials that have melting point over 3000℃.Chemically,nearly all UHTCs are borides,carbides,and nitrides of early transition metals(e.g.,Zr,Hf,Nb,Ta).Within the last two decades,except for the great achievements in the densification,microstructure tailoring,and mechanical property improvements of UHTCs,many methods have been established for the preparation of porous UHTCs,aiming to develop high-temperature resistant,sintering resistant,and lightweight materials that will withstand temperatures as high as 2000℃for long periods of time.Amongst the synthesis methods for porous UHTCs,sol–gel methods enable the preparation of porous UHTCs with pore sizes from 1 to 500μm and porosity within the range of 60%–95%at relatively low temperature.In this article,we review the currently available sol–gel methods for the preparation of porous UHTCs.Templating,foaming,and solvent evaporation methods are described and compared in terms of processing–microstructure relations.The properties and high temperature resistance of sol–gel derived porous UHTCs are discussed.Finally,directions to future investigations on the processing and applications of porous UHTCs are proposed.

Grain oriented growth and properties of ultra-high temperature CaBi_2Nb_2O_9 piezoelectric ceramics

CaBi2Nb2O9 (CBNO) ceramics was prepared at 1050℃ using regular flake-like CBNO powders as the precursor, and synthe-sized by the molten salts synthesis method. The tropism degree and microstructure of the ceramics were analyzed, and the die-lectric, ferroelectric and piezoelectric properties were characterized. Compared with conventional methods, the properties of CBNO ceramics by the new preparation method were found to be better. As the sinter temperature decreases, the grain growth becomes regular with textured features. The polarization process becomes easy to be realized at room temperature. Moreover, the dielectric loss decreases and the piezoelectric constant increases significantly.