As the development of hypersonic aerospace technology progresses, greater challenges are presented for solid rocket motors (SRMs) thermal protection, and the ablation performance of insulation materials needs to be further improved. Carbon nanotubes (CNTs) as a new type of reinforcing nano-filler, readily react with the oxidative components in the working gas during SRMs operation, limiting their excellent performance. In this study, we propose to coat the commonly used reinforcing filler, SiO2, on the surface of CNTs to suppress their susceptibility to oxidation and investigate the effects of adding CNTs, SiO2, and CNTs@SiO2 to the matrix on material properties. The results show that the addition of CNTs@SiO2 significantly improves the ablation resistance of the insulation material, with the linear ablation rate of M-@SiO2-2 being 56 % lower than that of MSiO2-2. Based on the analysis of the material's antioxidation performance and the strength of the resulting char layer after ablation, the reasons for the improvement of ablation performance are discussed. By conducting hightemperature tube furnace tests, the composition and structure of the char layer at different temperatures are studied, and it is found that CNTs in the CNTs@SiO2 formulation can directly provide the carbon source required for the carbon thermal reduction reaction, promoting the directional growth of SiC whiskers. Based on these findings, an ablation mechanism is proposed.

Carbon Nanotubes (CNTs) reinforced Polymer-Matrix Composites (PMCs) is widely used as insulation materials in thermal protection system of aerospace propulsion. However, CNTs are prone to oxidation and have high thermal conductivities, which makes it difficult to improve the ablation resistance of insulation materials that contain CNTs. SiO2 was encapsulated onto the surface of CNTs (CNTs@SiO2), which were then added to Ethylene Propylene Diene Monomer (EPDM) rubber to prepare the insulation materials. Thermogravimetric analysis and ablation test were used to evaluate the resistance of the insulation materials to thermal oxidation and ablation. Additionally, scanning electron microscopy was performed to analyze their microstructures. Results revealed that the addition of CNTs@SiO2 could visibly reduce the effects of hot corrosion and ablation on insulation materials. The C-CNTs@SiO2-1 formulation had the best ablative resistance. Further, compared with the unencapsulated formulation (C-CNTs-10), the C-CNTs@SiO2-1 formulation reduced the line ablation rate by 51% to 0.0130 mm/s after oxygen-acetylene experiments. Lastly, the ablation mechanism was investigated based on the effects of the CNTs@SiO2 additive on their properties. Thus, the improvement in ablation performance may be attributed to CNTs@SiO2-induced decreases in thermal conductivity, improvement in the hot corrosion resistance in the char layer, and changes in the microstructure.

The limited plasticity and poor formability of TiAl alloys constitute primary constraints on their widespread applicability. In this regard, an innovative forming method is proposed, characterized by the direct forging of unconsolidated pre-alloyed Ti–48Al–2Cr–2Nb powders. In this procedure, spherical powders with a broad particle size distribution are pre-encapsulated and subjected to vacuumed treatment, followed by direct high-temperature forging to attain the final desired shape. Throughout the process, the powders undergo pre-heating to various forming temperatures and are forged at different speeds, enabling a comparative analysis of the effect of forging temperature and speed on densification and the microstructural characteristics of the forged billet. Experimental results indicate that the powders can be nearly fully densified when direct forging is conducted within the α-phase region. By combining the finite element modeling and microstructural characterization, three mechanisms dominating the consolidation process of powders are revealed. Initial particle clustering and spatial rearrangement predominantly occur during the early deformation stage, enhancing densification. Subsequent fragmentation of particles, induced by severe plastic deformation, governs the entire deformation process, leading to the elimination of the prior particle boundaries and substantial densification improvement. The closure of the micrometer-scale voids is controlled by high-temperature diffusion and creep, which plays a pivotal role in weakening the detrimental effect of micro defects on mechanical properties. The above mechanisms act alternately or simultaneously, resulting in a homogeneous microstructure composed of α2+γ lamellae and bulk γ with small sizes, and a good synergy of strength and ductility. Therefore, this novel approach holds considerable potential as a cost-effective alternative strategy for producing TiAl components.

Hot working of titanium alloys within the (α+β) field is characterized by inherent multi-hierarchical heterogeneous deformation, with the two phases exhibiting distinct deformation characteristics while mutually influencing each other. In this study, systematic uniaxial isothermal compression experiments and crystal plasticity finite element modeling considering morphological characteristics were employed to deepen our understanding of the interactions between α and β phases during hot deformation. The impact of α deformation on the β phase was found to be closely associated with its morphology, distribution, feature size and α/β interface relationship. Primary equiaxed α grains exerted a double-edged effect on the deformation of the β phase. The activation of cross-slip in the β phase, coupled with the predominant pinning effect at β grain interior, collectively resulted in relatively homogeneous plastic deformation in the β phase. This elucidated limited β grain refinement observed in the equiaxed microstructure. Multiple deformation mechanisms in the lamellar microstructure were comprehensively analyzed by considering the active slip systems, slip transfer across phase interfaces and inter-colony interactions. Discrepancies in the activation of slip systems and slip transfer across α/β interfaces led to deformation heterogeneity at the lamellae scale. Notably, lamellar kinking manifested a synergistic effect in accelerating substructure formation in α and β phases. Interactions between colonies induced intense deformation gradients across the colony interface and thus triggered localized dynamic recrystallization, which was highly dependent on the relative orientation relationship of neighboring colonies. Heterogeneous deformation of the lamellar microstructure demonstrated great potential for refining microstructure and weakening microtexture in the β phase. This work offers fresh insights into the intricate interactions between α and β phases during hot deformation, providing a foundation for optimizing the thermomechanical processing of titanium alloys.

This study investigated the diagnostic performance of dual-energy computed tomography (CT) and deep learning for the preoperative classification of equivocal lymph nodes (LNs) on CT images in thyroid cancer patients. In this prospective study, from October 2020 to March 2021, 375 patients with thyroid disease underwent thin-section dual-energy thyroid CT at a small field of view (FOV) and thyroid surgery. The data of 183 patients with 281 LNs were analyzed. The targeted LNs were negative or equivocal on small FOV CT images. Six deep-learning models were used to classify the LNs on conventional CT images. The performance of all models was compared with pathology reports. Of the 281 LNs, 65.5

The realization of lightweight insulation materials is often accompanied by a decrease in ablation performance. Coordinating the contradiction between lightweight and ablation resistance is the key to the development of thermal protection technology. Addressing the need for high-performance insulation materials within solid rocket motors (SRMs) combustion chambers, we designed three multilayer composite structural insulation materials and studied their properties. The results show that among these constructed multilayer composites, the bilayer structure exhibited the lowest density at a mere 0.72 g/cm3, marking a 27% reduction compared to the basic structure. Remarkably, the bilayer configuration demonstrated superior ablation resistance, showcasing a 25% decrease in the line ablation rate in contrast to the basic structure after oxygen-acetylene test. This achievement embodies the successful harmonization of lightweight properties with ablation resistance. Furthermore, based on the performance and microstructure of the char layer, a further analysis revealed the enhancement mechanism of ablative performance by the multilayer composite structure. It was found that the synergistic effect of the compact/porous structure of the char layer grants the bilayer structure thermal insulation material optimal ablative performance. This work provides strong support for improving the performance of SRMs.Highlights Insulation materials with multilayer composite structures are designed. The materials exhibit both lightweight and superior ablation resistance. Compact/porous char layers enhance material ablation performance. Density and ablation properties of thermal insulation materials with different structures. image

The p-type Te-free Cu3SbSe4 with famatinite structure is a potential candidate for thermoelectric materials due to the low cost and eco-friendly constituent elements. However, its strong bipolar effect and high lattice thermal conductivity (klat) are the main challenges for its performance enhancement. Herein, we report a new strategy to enhance its figure of merit zT -0.86 at 673 K for Cu3Sb0.95Fe0.05Se2.8S1.2 via band structure tuning and hierarchical architecture. Firstly, S substituted Se atoms in lattice can widen the band gap to alleviate the bipolar effect. Secondly, Fe doping in Sb site significantly increases the density of states, thus increasing the carrier effective mass, and obtaining a remarkably high Seebeck coefficient of -560 mV/K at 300 K. Moreover, the induced hierarchical architecture defects resulting in a minimum klat of -0.48 W center dot m �1 center dot K-1 at 673 K. Consequently, the improved Seebeck coefficient combined with low thermal conductivity leads to an enhanced zT. (c) 2023 The Authors. Published by Elsevier B.V. on behalf of The Chinese Ceramic Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Lamellar kinking, a complex and significant cross-scale heterogeneous deformation behavior during primary hot working of titanium alloys, affects the microstructure evolution, mechanical response as well as optimization of product performance. However, the essence, development processes, formation condition, and contribution of kinking are still controversial. To address these issues, a two-scale crystal plasticity model is developed to analyze the intra-colony strain partitioning and inter-colony interaction. In-situ laser confocal microscope experiments with detailed microstructure characterization enable to track the origin and evolution of lamellar kinking. Kinking is re-recognized as deformation banding rather than the conventionally claimed instability resulting from elastic or plastic buckling or macro plastic flow. Strain partitioning plays a pivotal role in the driving force of kinking by stimulating the continuous orientation softening and leading to a decrease of strain energy. The dependence of kinking's formation condition on geometrical orientation can be rationalized by the orientation sensitivity of strain partitioning. The formation of kinking contributes to reducing the deformation resistance of colony with initially "hard" orientation and further improve the deformation compatibility among colonies. This work provides new insight into the cross-scale mechanisms of lamellar kinking, which can be utilized to control microstructure homogeneity during hot deformation of titanium alloys aiming at optimizing the performance of forging pieces.

The present study evaluated the β recrystallization behavior and deformation microtexture evolution of TB6 titanium alloy (Ti-10V-2Fe-3Al) taking place during isothermal compression. The hot deformation tests were carried out in the temperature range below the β phase transition temperature and spanned a wide strain rate range of 0.0001~1 s−1. Microstructure evolution on β phase, including its recrystallization behavior and microtexture formation, is sensitive to the strain rates, whereas the average grain size of equiaxed α phase exhibits a slight increase with the strain rate decreasing. Moreover, β recrystallization is not homogeneous among the prior β grains, and is characterized by: (I) enriched β sub-grains, (II) sporadically or chain-like distributed recrystallized β grains with a grain size far less than the prior β grains, and (III) wave-shaped β grain boundaries. The β recrystallization is inadequate and its orientation takes on the inheritance characteristic, which makes the β microtexture significant after deformation. At a lower strain rate, the high activity of the {11−2}<111> and {12−3}<111> slip systems induced the crystal rotation around <101>, but such crystal rotation did not destroy the Burgers orientation relationship (BOR), which could be accounted for by the generation of a strong microtexture of <001>//RD. The divergences on β recrystallization fraction, the operation of slip systems, and initial crystal orientations explain the different microtexture components with varied intensities under different deformation conditions.

塑性流动失稳是金属材料热变形过程中调控微观组织均匀性、 提高构件综合力学性能面临的关键基础性问题.对金属材料热变形过程中流动失稳相关的实验和建模方面目前所取得的研究进展进行了综述和分析,指出塑性流动失稳的主要类型有局部流动、 宏观剪切带和微裂纹,并且分别分析了不同类型失稳的形成机理;对变形温度、 应变速率、 变形量及变形前的微观组织对不同类型流动失稳的影响规律进行了总结;从理论和应用两方面,对现有的流动失稳预测准则和模型进行了总结和比较.此外,针对金属材料热成形,如何实现复杂加载路径下考虑变形前组织非均质性影响的流动失稳预测将成为今后发展的一个重要方向.

The hot ductility tests of a kind of 980 MPa class Fe-0.31C (wt pct) TRIP steel (TRIP980) with the addition of Ti/V/Nb were conducted on a Gleeble-3500 thermomechanical simulator in the temperatures ranging from 873 K to 1573 K (600 °C to 1300 °C) at a constant strain rate of 0.001 s −1 . It is found that the hot ductility trough ranges from 873 K to 1123 K (600 °C to 850 °C). The recommended straightening temperatures are from 1173 K to 1523 K (900 °C to 1250 °C). The isothermal hot compression deformation behavior was also studied by means of Gleeble-3500 in the temperatures ranging from 1173 K to 1373 K (900 °C to 1100 °C) at strain rates ranging from 0.01 s −1 to 10 s −1 . The results show that the peak stress decreases with the increasing temperature and the decreasing strain rate. The deformation activation energy of the test steel is 436.7 kJ/mol. The hot deformation equation of the steel has been established, and the processing maps have been developed on the basis of experimental data and the principle of dynamic materials model (DMM). By analyzing the processing maps of strains of 0.5, 0.7, and 0.9, it is found that dynamic recrystallization occurs in the peak power dissipation efficiency domain, which is the optimal area of hot working. Finally, the factors influencing hot ductility and thermal activation energy of the test steel were investigated by means of microscopic analysis. It indicates that the additional microalloying elements play important roles both in the loss of hot ductility and in the enormous increase of deformation activation energy for the TRIP980 steel.

It is hard for vehicles to move on the moon surface and the wheels of lunar rovers are easy to slide.It is significant to research on the vehicle-terramechanics on bumpy terrain,and the higher capabilities for locomotion systems are required.The wheel-terrain interaction model based on the soil's press-sinkage and shear theories from Bekker and Jonasi is established considering the effect of wheel lugs and the influence on stress distribution in shallow layer soil caused by the slope angle.The factors affecting traction performance are studied and the calculation results indicate that the drawbar pull and impeditive torque are affected by the slope angle,the radius,the width,the slip ratio of the driving wheel and the height of wheel lugs,and the drive efficiency reaches the maximum in an optimal interval of slip ratio.The references to lunar rovers' design and control are provided.

A simulation model of the drive system including a two-phase hybrid stepping motor module,a subdividing module,inverter bridges and current controlling modules was constituted based on Simulink to provide referrences to fault diagnosis.The natural operation and the faults including short circuit and open circuit in power transistors of H bridges were simulated and the performance waveforms relevant to different faults were obtained.Results of fault simulation were analyzed theoretically and the referrences to fault diagnosis of stepping motors are provided.

Ceramic coating was deposited on TiAl alloy substrate by micro-arc oxidation (MAO) in a silicate-aluminate electrolyte solution with additives including sodium citrate, graphite and sodium tungstate. The microstructures and compositions were analyzed by SEM, EDX and XRD. The corrosion and wear properties of the coatings were investigated by potentiodynamic polarization and ball-on-disc wear test, respectively. The results show that the MAO coatings consist of WO3, Ti2O3, graphite and Al2O3 besides Al2TiO5 and Al2SiO5. With additives in the electrolyte, the working voltage at the micro-arc discharge stage decreases, and the ceramic coating gets smoother and more compact. The corrosion current density of MAO coating is much lower than that of TiAl substrate. It can be reduced from 9.81×10−8 A/cm2 to 3.02×10−10 A/cm2. The MAO coatings composed of hard Al2O3, WO3 and Ti2O3 obviously improve the wear resistance of TiAl alloy. The wear rate is −3.27×10−7 g/(N·m).

Aluminum films were deposited on TiAl alloy by multi-arc ion plating(MAIP) and subsequently diffusion-treated under 720 ℃ for 4 h.The microstructure,chemical composition and phases of the films were analyzed by SEM,EDX and XRD.The microhardness and high temperature friction and wear behavior of the films were tested.The results show that the multi-arc ion plating aluminum films are compact and consist of Al.The aluminium films are transformed to the films composed of outer Al2 O3 layer and inner TiAl3 layer after diffusion treatment,and microhardness and high temperature wear resistance of the films are improved obviously.

在直流电机转动惯量的研究中,当负载的转动惯量是电动机的转动惯量2个以上数量级时,永磁无刷直流电动机（BLDCM）在启动以及加、减速时,会产生很大的惯性转矩,调速系统的性能将变差。为了系统的稳定性和保证运转速度,分析研究了BLDCM的数学模型和超大惯量负载的特性,提出了模糊PID控制方法。在Matlab/Simulink中建立了控制系统的仿真模型,进行了仿真实验,仿真结果可以表明,采用模糊PID控制方法系统在调速过程中,超调较小,响应速度快,稳态时无误差。证明模糊PID控制方法适用于BLDCM驱动的大惯量负载调速系统。

As one of the three components of a brushless DC motor(BLDCM),Hall position sensors were used to detect rotor position which provided commutation signals for electrical switches,so its performance directly affects the motor's running.This paper investigated the influence on BLDCM due to failure and postion error of Hall sensors,and established simulation model of the BLDCM with Matlab to carry out the simulation.At last,the phase currents and torque waveforms of the motor in the two states above were given.

A brushless DC motor drive system model based on Simulink with Hall sensors is constituted to provide references to fault diagnosis.The faults including short circuit,open circuit in power transistors and phase-fault in Hall sensors are simulated and performance waveforms relevant to different faults are obtained.Results of fault simulation are analyzed theoretically and references to fault diagnosis of brushless DC motor are provided.

Method of parametic design and secondary development technology of AutoCAD were introduced.A switched reluctance motor CAD system under the fashionable platforms of Microsoft Visual Basic 6.0 and Microsoft Access 2003 which can realize the automatic drawing was developed.The system has succinct GUI and the result of application shows that the actualization of parametric drawing can improve efficiency observably and reduce the burden on repetitive work and the lead-time of motors.

Current-flux linkage curves in the switched reluctance motors(SRM)were important for analyzing inherence parameters of SRM and the analytic arithmetic was adopted frequently for calculation of the curves in engineering.The analytic arithmetic was analyzed in the paper and some formulas were ameliorated.Comparison with the result of the finite-element software simulation demonstrates that ameliorated analytic arithmetic can improve operational precision and provide theoretic gist of analyzing electromagnetic parameters in the SRM.