Good High Temperature Research Articles

Preparation and Properties of Flexible Phenolic Silicone Hybrid Aerogels for Thermal Insulation

In order to prepare flexible thermal protection aerogel materials, using dimethyldimethoxysilane (DMDMS) and methyltrimethoxysilane (MTMS) as co-precursors, isocyanate-propyltrimethoxysilane (CFS-006) was added to the co-precursor as a coupling agent, and resorcinol and formaldehyde were added to the sol solution to prepare a phenolic silicone hybrid aerogel (FAS) by the sol–gel method. The prepared FAS aerogel had no phase separation problem, the density was only 0.118 g/cm3, the hydrophobic angle reached 155.3°, and it had certain flexibility. It could be compressed to 70% and still be restored to its original state. The FAS aerogel also had a low thermal conductivity of 0.0318 W/(m·K) and good high temperature insulation. The introduction of phenolic groups improved thermal stability; Tmax increased to 643.7 °C, and the residual carbon rate was 24.5%. This work has positive significance for the future combination of aerogels and textiles in the preparation of firefighting protective clothing.

A novel Ta-contained TiAl alloy with excellent high temperature performance designed for powder hot isostatic pressing

TiAl alloys offer strong potential for replacing conventional nickel-base alloys in structural applications at high temperatures, which requires good high temperature performance. This study analyzes the creep performance and thermal exposure characteristics for a powder hot isostatic pressing (P-HIP) Ta-contained TiAl alloy. The microstructure characteristics, creep performance, and thermal exposure properties of the nearly lamellar (NL) alloy with a size of about 145 μm were investigated. The alloy remains 0.72 % fracture strain at room temperature after exposure at 750 ℃ for 1000 h. The fitting results of creep curves show that the creep stress index n is 15.82 at 750 ℃, indicating the power law creep mechanism. By reducing the interfacial energy, Ta can facilitate the formation of metastable structures and achieve refinement. The enrichment of Ta element at the lamellar edge, both observed after thermal exposure and creep, inhibits the growth of lamellae and hinders the expansion of cavities due to its low diffusion rate, improving the thermal stabilities and creep performance. The P-HIP Ta-contained TiAl alloy shows exciting high temperature performance.

Damage evolution analysis of C/SiC screwed/bonded hybrid joints based on in-situ micro-CT technique

Due to own good high temperature mechanical properties, the C/SiC screwed/bonded hybrid joints are considered as an important development direction of vehicle connection structures. However, the difficulty of directly monitoring the interior of the hybrid joints during the bearing presents a potential challenge to the structural damage assessment. In this study, the damage process of the hybrid joints subjected to tensile loading was monitored and characterized based on the in-situ micro-CT technique. The intrinsic relationship between the mechanical responses of the hybrid joints and the local damage evolution was elucidated by observing the variation of the deposited SiC void volume at the overlap interface. The dual inhomogeneity of SiC bonding layer was quantitatively characterized utilizing the average failure rate and determination coefficient. The coupling influence mechanism of prefabricated bottom hole size and online connection process on the final assembly clearance was revealed.

Bond-Based Peridynamic Model for Tensile Deformation and Fracture of Polycarbonate and Polypropylene

Fracture mechanics has been a crucial aspect in the field of engineering science as technologies are rapidly growing nowadays. Various numerical methods have been developed to analyze fracture behaviour in different types of materials used in industries. Meanwhile, the application of polymers garners attention worldwide due to outstanding characteristics such as good strength, lightweight, and high temperature resistance, exemplified by polymers like polycarbonate (PC) and polypropylene (PP). Hence, failure aspects of such materials must be taken into consideration when conditions arise that may lead to failure, such as high-load impact, fatigue, and extreme temperatures. In this study, a bond-based Peridynamic model (PD) for the tensile behaviour, including fracture, of polymers has been developed. The PD model is constructed using the Centos software and encompasses both brittle and ductile fracture behaviours. Numerical results, including crack propagation, damage zone, and force-extension curves of notched specimens, are validated by comparison with experimental results of PC and PP. Through the validation process, PC specimens exhibit a difference percentage range for maximum load and rupture extension of 2.9% to 18.8% and 2.4% to 4.6%, respectively. PP specimens show a difference percentage range for maximum load and rupture extension of 31.2% to 43.5% and 0.9% to 30%, respectively. Consequently, the validation results indicate that the PD model for brittle specimens aligns more closely with experimental data compared to the PD model for ductile specimens.

Anti-oxidative quartz/carbon-braided fiber reinforced ceramizable composites modified with B4C and AlB2: Mechanical robustness, phase evolution and anti-oxidation mechanism

Carbon fiber reinforced ceramizable phenolic resin matrix composites (Cf/CPR) have been widely used in the field of thermal protection materials. However, the industrial application of the Cf/CPR is restricted by its easy oxidation failure under high temperature condition. In this work, a novel antioxidative ceramizable composites modified with AlB2 and B4C (Cf-Qf/CPR) were prepared by using quartz fiber-coated carbon fiber (Cf-Qf) as reinforcements via co-weaving technique. The thermal stability, mechanical properties, interfacial phase evolution and anti-oxidation mechanism of the composites were investigated. The residue yield and the flexural strength of the composites after treatment at 1200°C for 15 min were 93.4 % and 62.4 MPa, increased by 5.4 % and 67.3 % compared with those of Cf/CPR. Quartz fiber and ceramic protective layer showed synergistic effect to improve the oxidation resistance of carbon fiber and PyC, confirming good high temperature mechanical properties and oxidation resistance of as-received composites.

First-principles calculations to investigate pressure effect on structural, mechanical, electronic and thermodynamic properties of NADFP·DMF

NADFP·DMF has good detonation performance, mechanical sensitivity and high thermal decomposition temperature. Current studies on NADFP·DMF have been carried out at ambient temperature and pressure, and its properties under pressure have yet to be analysed in depth. By using the generalized gradient approximation (GGA) plane-wave norm conserving pseudopotential method based on the framework of density functional theory, the structural, mechanical, electronic and thermodynamic properties of the monoclinic crystal system NADFP·DMF under 0–20 GPa are calculated. The calculations show that the lattice parameters decrease with increasing pressure. The structure is mechanically stable and ductile within 0–20 GPa. We analyzed electronic properties, including band structure and density of states. NADFP·DMF is a direct band gap compound only at 15 GPa, and the band gap decreases with increasing pressure, resulting in an increase in sensitivity. In addition, the thermodynamic properties of NADFP·DMF are investigated, including enthalpy, temperature*entropy, Gibbs free energy, Debye temperature and heat capacity.

Effects of Y doping on phase structure, mechanical properties and sintering behavior of (Yb1-xYx)2SiO5 environmental barrier coating materials

Yb2SiO5 is one of the most widely studied environmental barrier coating materials due to its excellent high-temperature phase stability and resistance to water oxygen corrosion. In this paper, a series of (Yb1-xYx)2SiO5 (x = 0, 0.1, 0.2, 0.3, 0.4) ceramics were fabricated by high-temperature solid state sintering at 1550 °C. The effects of Y doping concentration on phase composition, mechanical properties, thermal conductivity and high-temperature sintering behavior of Yb2SiO5 ceramics were investigated in detail. The results show that all the (Yb1-xYx)2SiO5 ceramic specimens are composed of single X2-Yb2SiO5 phase with relative high compactness. The introduction of Y gives rise to the reduction of the thermal conductivity of Yb2SiO5 and the value of cell parameters and volume of (Yb1-xYx)2SiO5 is proportional to the Y3+ doping concentration. Among the five (Yb1-xYx)2SiO5 ceramics, (Yb0.9Y0.1)2SiO5 possesses the lowest brittleness index and its average fracture toughness is 2.85 MPa m1/2, which is about 10 % higher than pure Yb2SiO5. In addition, (Yb0.9Y0.1)2SiO5 has good high temperature phase stability from room temperature to 1450 °C and the grain size of (Yb0.9Y0.1)2SiO5 is basically unchanged after sintering at 1400 °C for 100 h. We believe that (Yb0.9Y0.1)2SiO5 is one of the most promising candidate materials for environmental barrier coatings.

Stable preparation of defective fluorite structure high entropy (Y0.2Sm0.2Eu0.2Er0.2Yb0.2)2Zr2O7 ceramic powders by molten salt synthesis

Rare earth zirconate ceramic has been considered as one of the potential thermal barrier coating materials to replace 6–8% YSZ material (6–8% yttrium oxide stabilized zirconia), because of its low thermal conductivity and good high temperature phase stability. However, there is a problem that the coefficient of thermal expansion does not match the matrix. In this paper, rare earth high entropy zirconate ceramic powder with defective fluorite structure was prepared by molten salt synthesis(MSS). The results show that the reaction temperature and the ratio of reactants to molten salt will affect the synthesis effects. With the action of the high entropy effect, the synthesized ceramic powder has low thermal conductivity, improved thermal expansion coefficient and high infrared reflectivity.

Achieving enhanced piezoelectric properties in BiFeO3-PbTiO3 based ceramics by a synergistic effects of texturing and structure engineering in reactive template grain growth-like process

A synergistic strategy of texturing and structure engineering in reactive template grain growth-like process has been validated on fabricating 0.66Bi0.9Sm0.1FeO3-0.34PbTiO3 piezoelectric ceramics with enhanced properties. A considerable texture degree is successfully obtained by optimizing sintering conditions. The template is fully dissolved into the matrix after sintering, driving a structure transformation from rhombohedral to pseudo-cubic phase. In comparison to its non-textured counterpart, the textured ceramics show a 69 % increase on large-signal piezoelectric coefficient d33* and a 43 % increase on small-signal piezoelectric coefficient d33. Good high temperature piezoelectric performance is also revealed. At 225 °C, the maximum strain and calculated d33* are 0.22 % and 436 pm/V, respectively, which increase by 49 % compared with corresponding parameters at room temperature. The study not only signify a promising strategy to design high performance BFO based functional materials, but also broaden the scope of texture technology in the development of piezoelectric ceramics.

Influence of thickness and surface roughness on impact wear and impact lifetime of HVOF-sprayed coatings

A number of industrial applications today require thermally sprayed coatings that exhibit good adhesion, high temperature and chemical resistance, and can withstand particle impacts or dynamic interactions with components. A common example of a high-velocity oxygen fuel (HVOF) sprayed coating with such the aforementioned properties is Cr3C2–25%NiCr. The objective of this study is to examine the impact of varying thicknesses and surface roughness on the impact lifetime and impact wear of Cr3C2–25%NiCr coatings. A series of Cr3C2–25%NiCr coatings were subject to analysis using a dynamic impact tester with impact loads of 200 N, 400 N, and 600 N. The results indicated that there exists an optimal coating thickness with the highest impact lifetime. The results were discussed using microstructural analysis of the impact coatings and finite element simulation. The maximum impact lifetime was achieved with the optimal combination of sample material properties, substrate mechanical properties, coating thickness, and residual stress. Furthermore, it was demonstrated that surface does not influence the impact lifetime of the coating, but does affect the accuracy of its determination.

Microstructure, wear and corrosion resistance mechanism of as-cast lightweight refractory NbMoZrTiX (X = al, V) high-entropy alloys

Refractory high-entropy alloys (RHEAs) have good overall properties and potential high temperature applications, but they are not competitive in terms of light weight and wear and corrosion resistance, which severely limits the wide range of applications. In this paper, novel NbMoZrTi-X (Al, V) light refractory high entropy alloys (LRHEAs) were fabricated and their physical phase composition, microstructure, hardness, and wear and corrosion resistance were systematically investigated. The results show that NbMoZrTi LRHEA and NbMoZrTiV LRHEA are both single BCC structures, while NbMoZrTiAl LRHEA and NbMoZrTiAlV LRHEA are transformed into BCC, B2, and Zr5Al3 phase structures. The hardness increases as the volume fraction of the Zr5Al3 hard phase increases, with NbMoZrTiAl LRHEA having a maximum Vickers hardness of 811.29 HV. Room temperature dry friction tests showed that NbMoZrTiAl LRHEA had the lowest wear and coefficient of friction of 1.5 mg and 0.6713, respectively. Electrochemical tests performed in 3.5 wt% NaCl solution showed that NbMoZrTiAlV LRHEA has excellent corrosion resistance with the highest Ecorr (−0.142 V) and the lowest Icorr (2.149 × 10−7 A/cm2). Therefore, the addition of V and Al to NbMoZrTi-based LRHEA can effectively improve its wear and corrosion resistance due to the increase in hardness and dense passivation film formation. Our study provides a new strategy for designing LRHEAs with a combination of high hardness and excellent wear and corrosion resistance.

Microstructure evolution and performance of TiMoCrWxTay refractory high-entropy alloy coatings prepared using laser cladding

Refractory high entropy alloy (RHEA) coatings containing W and Ta elements at the same time usually have excellent performance at high temperature, which are promising candidate materials for high temperature protective coating materials. In this work, the effects of W and Ta on the microstructure and performance evolution of TiMoCrWxTay RHEA coatings have been investigated. Experimentally, TiMoCrWxTay coatings are mainly composed of BCC phase, Laves phase and Ti-rich phase, with W and Ta atoms preferably dissolved in BCC phase. The W atoms promote the formation of dendrites and the growth of rod-like and equiaxed crystals and the Ta atoms promote the formation of cellular crystals and produce the effect of fine crystal strengthening. W and Ta atoms have significant influence on the tribological properties of TiMoCrWxTay coatings. The tribological properties of TiMoCrWxTay coatings at 800 °C are better than those at room temperature. TiMoCrWxTay RHEA coatings follow near-linear oxidation kinetics during the oxidation of 50 h at 800 °C.The oxidation resistance of the coatings first increases and then decreases with the increase of Ta content. Ta2O5, TiO2 and other oxides may have a shielding effect on the oxidation of W. In particular, The W0.3Ta0.5 shows the best tribological properties and oxidation resistance, and the mass gain of W0.3Ta0.5 is only 13.4 mg/cm2 after the oxidation test for 50 h. It indicates that TiMoCrWxTay coatings can obtain good high temperature performance by optimizing the content of W and Ta in RHEA coatings. This work can provide guidance for the research and application of TiMoCrWxTay RHEA coatings.

Ultralow-loss soft magnetic composites with temperature-resistant and insulated Al2O3/SiO2 layers through pyrolysis

Soft magnetic composites (SMCs) with low power loss are urgently needed to meet the increasing demand for high frequency and miniaturized inductors and transformers. Ultrathin cladding with good insulation and high temperature resistance is the key to achieve low-loss SMCs. In this study, we used MQ silicon resin as precursor to produce in-situ grown Al2O3/SiO2 composite insulating layer in FeSiAl SMCs through pyrolysis process and high-temperature reaction. The morphologies, microstructures and compositions of the coatings on the surface were characterized by SEM, TEM, EDS, TG, XRD, FTIR and XPS, and the results show FeSiAl powders are evenly and entirely covered with an inner Al2O3 and outer SiO2 composite insulating layer. The results of powder resistivity show that the insulating layer still maintains very high resistance after annealing at 750 °C. The composite insulating layer had high resistivity and reduced eddy current loss, while the high temperature annealing process reduced stress and defects and resulted in low hysteresis loss. The best magnetic properties were obtained from samples coated with 2.0 wt% MQ and annealed at 750 °C, with an effective permeability of 76 and the lowest power loss of 72.2 mW/cm3 at 50 mT/100 kHz, 88.5 mW/cm3 at 100 mT/50 kHz and 304.1 mW/cm3 at 100 mT/100 kHz.

Synthesis and Photophysical Properties of Bipolar Compound: Triphenylamine/Diazafluorene-Carbazole.

Carbazole and triphenylamine, are two well-known hole transporting units that are attached to electron transporting unit 4,5-diazafluorene in a fascinating way to bring out non-planar configuration of a molecule. The synthesized compound exhibits good thermal stability (Td > 515°C) and high glass transition temperature (Tg, 191°C). Optical bandgap (Egopt) obtained from solid state absorption spectra was calculated to be 2.93eV. Solid state photoluminescence spectra displays the emission maxima at 473nm. The emission characteristics of the compound observed in solvents of different polarity confirms the existence of intramolecular charge transfer in their excited state. Density functional theory studies reveal that HOMO and HOMO-1 localized on triphenylamine is spatially separated from LUMO of 4,5-diazafluorene, which manifest its bipolar character. The realization of long lived charge separated state upon photo-excitation from time resolved photoluminescence studies ascertains the charge transfer from triphenylamine to 4,5-diazafluorene. The experimental and theoretical analysis of the compound proved it to be a promising candidate for the fabrication of OLED devices.

A Novel Hexagonal Close-Packed High-Entropy Alloy with Outstanding Strength-Ductility Synergy

Refractory high-entropy alloys (HEAs) are new potential candidates in high temperature applications. However, most present refractory HEAs are single-phase body-centered cubic (BCC) structure, which is brittle at room temperature. Then strategies to ductile the refractory HEAs and maintain their good high temperature strength at the same time should be under consideration. In the present study, a novel WReOsIr HEA with hexagonal close-packed (HCP) structure was developed. This alloy not only has excellent high-temperature strength (416.7 MPa at 1473 K), but also exhibits good ductility (30.7%) at room temperature. The better room temperature plasticity is found to originate from the deformation twins formed inside the grains.

Preparation and thermal insulation performance of Al2O3[sbnd]Y2O3[sbnd]SiO2 ternary composite aerogels with high specific surface area and low density

Against the background of global energy shortages and the need for long-term flight safety of aerospace vehicles, traditional silica aerogels have the problems of insufficient temperature resistance and poor thermal insulation at high-temperatures, and are no longer able to meet the demand. In this study, a series of monolithic Al2O3Y2O3SiO2 ternary aerogels were successfully synthesized via synchronous sol–gel and ethanol supercritical drying. Both the prepared aerogels and the calcined samples at 1000 °C exhibited a complete three-dimensional network structure and a high specific surface area (up to 675.7 m2/g and 214.4 m2/g), which was attributed to the supporting effect of the Al2O3 component on the overall skeleton and the inhibiting effect of the Y2O3 component on the crystal transformation. Mullite fiber reinforced Al2O3Y2O3SiO2 aerogel composites were synthesized by vacuum impregnation using mullite fiber felt as a matrix. The prepared sample exhibit very low thermal conductivity (as low as 0.079 W⋅m−1·K−1 at 1000 °C). In summary, the good structural stability and high temperature thermal insulation performance make Al2O3Y2O3SiO2 ternary aerogel have the potential of efficient service in more application scenarios. This study provides a product optimization reference idea for the thermal insulation material industry.

Design and competitive growth of different spinels at 750 °C for the multi-component CuCoMnFe alloy coatings

The diversified MnCoCuFe coatings can enhance the thermal growth stability and sintering property of spinel, and the multicomponent spinel exhibits good high temperature conductivity. The oxidation products of seven composite alloy coatings at 750 °C, CoNi(Fe), CoMn(Fe), CoMnCu(Fe), MnCu(Fe), MnCuCo(Fe), CuCoMn(Fe) and CuCo(Fe) coatings, were discussed in details. Due to differences in the elements and their concentrations in the designed coatings, some coatings could produce spinel, while others did not. The designed CuCo(Fe) coating and CuCoMn(Fe) coating prepared by electrodeposition in this study with the concentration ratio approximately nCu:nCo:nMn≈1:1:1. The oxidation reaction equations for the CuCoMnFe coating and CuCoFe coating at 750 °C were discussed. CoFe2O4 spinel was preferentially formed in the CuCoFe coating and CuMn2O4 spinel was preferentially formed in the CuCoMnFe coating. Both coatings demonstrated the good high-temperature oxidation resistance and high-temperature electrical conductivity.

Research on Ultrasonic Vibration Assisted Grinding Technology of Quartz Fiber Reinforced Ceramic Matrix Composites

Ceramic matrix composites have good mechanical properties and high temperature resistance, but it is difficult to process. In order to solve the problems of fast tool wear and low machining efficiency in the dry grinding process, ultrasonic vibration assisted grinding technology of quartz fiber reinforced ceramic matrix composites is adopted in this paper. Grinding force, machining efficiency, tool wear and surface roughness are analyzed through the comparison experiment between the conventional grinding and the ultrasonic vibration assisted grinding. The influence of the ultrasonic vibration assistance and process parameters on machining quality and tool life is further obtained. According to the findings, when compared to traditional grinding, ultrasonic vibration grinding can lower the grinding force by 25% to 58% and the surface roughness by up to 16%. The tool life and machining efficiency can be significantly increased with the help of ultrasonic vibration.

Design and preparation of sandwich structured Si3N4 ceramics for broadband microwave transmission

To develop high-temperature structural materials with broadband microwave transmission ability used for high-speed aircraft radome, a sandwich-structured silicon nitride (Si3N4) ceramic consisting of porous core and dense shell is designed based on CST simulation, which helps to obtain the optimized structural and dielectric properties. After that, its near-net-shape preparation strategy is presented by a controllable combined process including gel-casting (GC), polymer infiltration and pyrolysis (PIP), and chemical vapor deposition (CVD). The mechanical and electromagnetic performances were studied. The results show that the optimally-structured sandwich Si3N4 processes a flexural strength of 216.5 MPa and a microwave transmissivity of 80 % in 2–13.4 GHz, which are obviously higher than that of traditional Si3N4 ceramics. Besides, this sandwich-structured Si3N4 ceramics also shows excellent dielectric and mechanical stabilities after a high-temperature oxidization at 1600 °C for 2 h in air atmosphere. Our prepared Si3N4 ceramics achieves excellent mechanical strength, high microwave transmissivity, and good high temperature stability, indicating a great application potential as high-speed aircraft radome materials.

Synergistic effect of Mn and B on the cohesive properties of grain boundaries in Ni3Al: A first-principles study

Ni-based superalloys are known as potential structural materials under extreme conditions due to their good high temperature properties. However, some alloys such as Ni3Al exhibit intrinsic brittleness which severely restricts their practical applications as structural materials. It is well known that the moderate addition of B can significantly improve the ductility of Ni3Al grain boundaries (GB) but restricted to the Ni-rich side. Adding Mn together with B can improve the ductility of Ni3Al in a wider composition range. To provide some fundamental understandings on such a cooperative effect, the segregation of Mn or/and B to the Ni3Al GBs and their effects on the cohesive properties of the GBs are systematically investigated by using a first-principles method. It is shown that B tends to segregate to the Ni-rich holes of the GBs, which means that B prefers to form stronger covalent bonds with the Ni atoms. The calculation of Griffith’s work shows its improved effect on the cohesion of the GBs. Different from site occupation tendency in bulk Ni3Al, Mn tends to segregate to the GBs and substitute the Ni sites at the GBs. It is interesting to notice that B can segregate to the Ni-deficient hole and improve the cohesive properties of the GBs in the presence of Mn substituting Ni atoms at the GBs. Whether at the Ni-rich holes or Ni-deficient holes of B segregation, Mn substituting the Al sites won’t take place at the GBs. The improvement of the ductility of composition-dependent Ni3Al extends from the Ni-rich side to the stoichiometric side with the co-doping of Mn and B. The electronic structure mechanism behind is discussed based on the calculated electronic density of states. It is suggested that the beneficial cooperative effect of Mn and B on the cohesive properties of the GBs is attributable to the increasing B-Al interaction.