中间相炭微球成型体热处理过程中的宏观性能

用中间相炭微球(MCMBs)为原料,冷模压成型,再经过热处理后得到高密高强模压炭/石墨材料.考察MCMB成型体在热处理过程中的宏观变化,探索其收缩规律.实验结果表明,在热处理过程中,MCMB成形体的炭化失重主要发生在低温处理阶段,900℃炭化失重已超过90%,而尺寸收缩主要发生在高温炭化阶段,其中热处理温度在900℃～2000℃阶段其体积收缩超过了总体积收缩的45%.     

冷拔小口径16MnNiV无缝钢管的显微组织与力学性能演变规律

16MnNiV钢由16Mn, 16MnV钢发展而来,棒坯经热穿孔轧制成为管坯后,再进行冷轧、冷拔和热处理,用于制备高强度小口径的高压油管。通过光学显微镜(OM)、扫描电子显微镜(SEM)、电子背散射衍射技术(EBSD)、透射电子显微镜(TEM)以及物理化学相分析法研究了在拉拔制管过程中小口径16MnNiV无缝钢管显微组织与力学性能的演变,揭示了其微观组织以及第二相析出的变化规律,并计算了其强化增量,相关结果可以为高强度高压油管的材料研制和性能提升提供参考。结果表明,实验钢在拉拔制管过程中的主要组织为铁素体与珠光体,随着冷拔工艺的进行,实验钢的有效晶粒尺寸呈现减小趋势。从析出情况来看,一次拉拔后退火会增加其析出总量,二次拉拔后退火不改变其析出总量。通过EDS分析得知,析出的第二相粒子为VC。经过冷拔过程以及不同的热处理工艺,实验钢的抗拉强度和屈服强度均逐渐增加,伸长率逐渐降低。强化机理计算可知,由于冷拔过程变形量较大,实验钢屈服强度的提高主要来自于细晶强化的贡献。?6.35 mm×3 mm圆管经过热处理后的抗拉强度达到960 MPa以上,屈服强度达到864 MPa,伸长率达到15.5%,...     

芯轴摩擦系数对推压-拉拔复合缩径的影响

推压-拉拔复合缩径工艺是管坯减径的新方法,芯轴外表面与管坯内表面之间摩擦系数对工艺有重要的影响。通过建立推压-拉拔复合缩径变形过程中变形管坯的力学模型,分析了芯轴外表面与管坯内表面之间摩擦系数对成形的影响规律。针对某载重6.5 t胀压成形汽车桥壳管件的第一道次推压-拉拔复合缩径,设定不同的芯轴摩擦系数,进行了有限元仿真,得到了芯轴摩擦系数对管坯变形的影响规律,并基于管坯传力区不失稳以及变形所需凹模推力和芯轴拉拔力较小,给出了芯轴摩擦系数的设定范围。进行了缩径实验,实验和有限元模拟的结果接近。较小的芯轴摩擦系数可能造成管坯起皱失稳,而较大的芯轴摩擦系数,有利于降低管坯轴向压应力、凹模推力和芯轴拉拔力,但可能造成管坯表面划伤。     

采用Fe－Al－Mn－O系热敏材料的温度报警铠装热敏电缆的研制

采用Ｆｅ－Ａｌ－Ｍｎ－Ｏ系热敏材料制备了用于大面积温度监测的铠装热敏电缆。其结构为：最外层为铠装金属管，金属管内为半导体的热敏材料，两根平行于金属管的电极丝埋在热敏材料中。所制得的铠装热敏电缆元件（每根６米长）在１００℃～３５０℃时的电阻值在１０￣１～１０￣５Ω范围内，材料常数Ｂ在４０００～６０００Ｋ，能够满足实用要求。该铠装热敏电缆具有良好的稳定性。在７２０ｈ３５０℃老化中，每隔７２ｈ测得的电阻值的最大变化为３．０％；在１００℃～３５０℃热循环中，电阻值变化在０．１～７．９％范围，对应的温度测量偏差为０．１～３．１℃。还对铠装热敏电缆沿长度方向的均匀性问题进行了探讨。     

氧化法热处理温度对氧化钒薄膜热敏特性的影响

采用直流磁控溅射法制备氧化钒薄膜,并采用不同的温度对其进行氧化法热处理,通过XRD、SEM、四探针薄膜电阻测试,分析了不同热处理温度对氧化钒薄膜的晶相特性与热敏特性的影响。实验分析证明热处理温度升高后(400℃)得到的薄膜热敏特性良好,其室温电阻为160KΩ·cm,室温电阻温度变化系数为-2.4%/℃,变温过程中(20~98℃)其平均值约-1.98%/℃,表明温度升高有利于改善薄膜热敏特性,在非制冷红外探测器应用方面具有发展潜力。     

聚酰亚胺薄膜制备高定向石墨材料的研究

将双向拉伸聚酰亚胺(PI)薄膜叠层、压制炭化、高温热处理后制得了高定向石墨材料.借助TG、元素分析、XRD等测试手段分析了PI薄膜层叠成型体在热处理过程中质量、尺寸、化学组成、微观结构的变化.结果表明成型体炭化期间薄膜面向收缩较大,层叠方向尺寸变化不大,对材料进一步加压石墨化后,发现材料沿层叠方向有较大收缩,沿径向收缩较小.XRD分析表明PI薄膜热处理过程中会发生从高分子定向膜到无定型炭,再到高有序石墨结构的转变.经2800℃处理后的材料具有高的取向性和传导性能,四探针法测得样品的电阻率为0.79μΩ·m,根据电阻率与热导率的相关公式推得其热导率为1000～1600W/m·K.     

奥氏体不锈钢焊缝组织等轴晶化处理方法的研究

为了改善焊管的耐腐蚀性和力学性能，将奥氏体不锈钢对接焊管经过拉拔减径预变形后，再用适当温度退火处理，从而使焊缝组织实现再结晶，即以不具方向性的等轴晶组织取代具有方向性很强的柱状晶（或柱状树枝晶）组织。结果表明，已等轴晶化的焊缝，不仅在组织形貌上变得和母材基本一致，而且耐腐蚀性也得到了提高。为了保证焊缝组织完全转变为细小的等轴晶组织，预变形量应在9．4％以上的减径率，并且最佳退火温区应在980-1000℃以内。     

贝氏体型冷作强化非调质钢的氢致延迟断裂行为

采用电化学充氢和慢拉伸应变速率实验(SSRT)研究了形变和时效处理对一种低碳-Mn-B-Ti系贝氏体型冷作强化非调质钢氢致延迟断裂行为的影响规律。结果表明,无论热轧态还是拉拔态试样,充氢后试样的耐延迟断裂性能显著降低。在拉拔变形初期,减面率γ<20%时,耐延迟断裂性能降低的幅度较大;而随着拉拔量的继续增加,耐延迟断裂性能降低的趋势变缓。实验料拉拔后进行时效处理有助于其耐延迟断裂性能的改善,当时效温度提高到200℃以上时这种改善作用比较明显。     

热等静压对第三代单晶高温合金DD33显微组织和持久性能的影响

对第三代DD33单晶高温合金进行标准热处理、热等静压以及不同制度的后续固溶和时效处理,并在850℃/650 MPa和1100℃/170 MPa条件下进行高温持久性能实验,使用金相显微镜(OM)、扫描电子显微镜(SEM)和X射线三维成像技术(XCT)等手段观察和表征不同状态的样品,研究了热等静压和热处理对这种合金显微组织和持久性能的影响。结果表明：铸态DD33单晶高温合金经过适当的热等静压和后续热处理工艺后,样品的组织形貌(γ′相尺寸、体积分数与立方化程度)与标准热处理态基本相同。与标准热处理态合金相比,热等静压处理后合金显微孔洞的体积分数和尺寸均显著降低,其体积分数从0.0190%降低到0.0005%,最大孔等效直径从36.9 μm减小到14.2 μm。在850℃/650 MPa和1100℃/170 MPa条件下热等静压后的样品持久寿命均显著延长。这表明,适当的热等静压和热处理能消除合金内部的显微孔洞缺陷,使其持久性能显著提高。     

焦耳热处理降低石墨烯/环氧树脂发热涂层的体积电阻率

石墨烯基发热涂层一项重要的用途是降低其体积电阻率。文中结合发热涂层本身可以产热的特点,对涂层施加电压让其产热来对涂层进行焦耳热处理以降低涂层的体积电阻率。首先研究了通电焦耳热处理后的涂层体积电阻率随处理温度、时间和周期的变化,然后用X射线衍射和扫描电镜说明了涂层体积电阻率降低的原因以及该过程与外热处理的区别,讨论了石墨烯含量、片径大小对处理后的涂层体积电阻率降低的影响,最后对处理前后涂层的发热温度进行了比较:对涂层进行130℃,30 min的处理后,涂层在60 V电压下,表面发热温度由67.6℃升高到120.4℃     

A Log-Antilog Analog Control Circuit for Constant-Power Warm-Thermistor Sensors— Application to Plant Water Status Measurement

Warm-thermistor sensors are useful for making measurements of flow and the thermal properties of materials. This paper describes a log-antilog analog control circuit capable of monitoring a thermistor's internal temperature in both ambient temperature sensing mode and self-heating mode, while maintaining infinite precision, wide dynamic range and fast sensor response. A single self-referencing thermistor is used to avoid the problems associated with having to match a thermistor pair in order to obtain an over-temperature signal. Instead, thermistor power levels are switched over a range of 1:1000, allowing measurement of both ambient temperature and heated thermistor temperature during the rise and fall of the heat pulse by a single thermistor at the center of the heat field. This provides a sensitive measurement of the thermal diffusivity and advective properties of the surrounding medium. In this paper, such a sensor is used to investigate the thermal properties of a grapevine cane under conditions of irrigation stress.      

Monitoring of the physical aging of radiation cross-linked conductive rubber blends containing clay nanofiller

Polymeric materials are widely used as insulation and jacketing materials in wire and cable. When such materials are used for long-term applications, they undergo thermal oxidation aging in the environment. It is necessary to develop an in situ and non-destructive condition monitoring (CM) method to follow the aging of cable materials. The main objective of this work was to investigate polymer composites as potential sensor materials for this purpose. Rubber/carbon black composites with a carbon black loading below the percolation threshold underwent accelerated thermal oxidation aging experiments. The results indicated that the substantial resistivity decreases of the composites could be directly related to the increases in volume fraction of the conductive carbon black, which was mainly caused by the mass loss of polymer matrix and sample shrinkage during the thermal oxidation aging process. Compared to existing CM method based on density change, the electrical resistivity is more explicit regarding its absolute changes throughout the thermal oxidation aging. The change in resistivity spanned over two orders of magnitude, whereas the composite density only increased 5%. The results offer strong evidence that resistivity measurements, which reflect property changes under thermal aging conditions, could represent a very useful and non-destructive CM approach as well as a more sensitive method than density CM approach.     

核电站电缆料的研究进展

依据核电站电缆的种类,介绍了核电站电缆料的种类、性能、生产工艺和国内外的研究现状。研究发现,制备核电站电缆绝缘料主要用交联聚乙烯(XLPE)和硅橡胶(或硅橡胶复合材料),此两种原料具有优良的耐热性、电绝缘性、耐低温性、耐化学性和良好的耐辐射性;核电站电缆料应具有低烟无卤、耐阻燃性和耐环境性能;其制备方法主要是挤出法,此方法生产工艺简单、成本低。最后展望了核电站电缆料的发展趋势。     

基于空腔辐射效应的钢索截面温度场分析

该文基于传热学基本理论及ABAQUS数值传热分析平台,以圆柱壁的截面径向导热热阻和空腔热阻代替平壁导热热阻,分别建立了四面受火工况下具有空腔几何特征的钢索截面升温理论及数值传热模型,得到考虑空腔辐射传热效应的无防火保护钢索截面升温历程,将其与具有等效截面圆钢的升温历程比较,研究表明:截面尺寸和空腔辐射效应对钢索截面升温历程有显著影响,空腔辐射效应在火灾升温初期加快了钢索截面的升温速率;最终在钢索热传导理论分析及数值模拟基础上,建议了钢索截面升温计算式,从而准确确定火灾升温历程中钢索材料性能衰减程度,正确评估预应力张拉结构中钢索的抗火承载力。     

High Volumetric and Gravimetric Capacity Electrodeposited Mesostructured Sb2O3 Sodium Ion Battery Anodes

Sodium ion batteries (SIBs) are considered promising alternatives to lithium ion batteries for grid‐scale and other energy storage applications because of the broad geographical distribution and low cost of sodium relative to lithium. Here, fabrication and characterization of high gravimetric and volumetric capacity 3D Ni‐supported Sb₂O₃ anodes for SIBs are presented. The electrodes are prepared by colloidal templating and pulsed electrodeposition followed by heat treatment. The colloidal template is optimized to provide large pore interconnects in the 3D scaffold to enable a high active materials loading and accommodate a large volume expansion during cycling. An electrodeposited loading of 1.1 g cm^?3 is chosen to enable a combined high gravimetric and volumetric capacity. At this loading, the electrodes exhibit a specific capacity of ≈445 mA h g^?1 and a volumetric capacity of ≈488 mA h cm^?3 with a capacity retention of 89% after 200 cycles at 200 mA g^?1. The stable cycling performance can be attributed to the 3D metal scaffold, which supports active materials undergoing large volume changes, and an initial heat treatment appears to improve the adhesion of the Sb₂O₃ to the metal scaffold.     

相变材料作为驱动力在航天器上的研究与应用

大多数相变材料由固相转变为液相时,吸收相变潜热,相变材料体积膨胀;从液相转变为固相时放出相变潜热,体积缩小。利用相变材料的这种体积随相变而变化的特性,将一定量的相变材料封装在密闭容器中,通过环境温度引起相变材料相变,相变过程中因体积变化产生的力,为某些需要微小位移量的运动机构提供驱动动力。最后,实例说明相变材料这种特性在航天器微驱动上的应用。     

热漏和有限热源对两源制冷机最优构型的影响

考虑一类存在热漏和低温热源有限的两热源制冷机，寻求其在给定循环周期和吸热量（也即给定制冷率）下制冷系数最大的最优构型，所述模型包括了４种特殊情形：（１）无热漏且无限热容低温热源；（２）无热漏但低温热源有限；（３）有热漏但低温热源无限；（４）有热漏且低温热源有限，分析中设传服从牛顿定律。结果表明，对无限热容热源情形，热漏的存在不改变循环最优构型，对无热漏情形，有限热容热源使循环构型的为某种“广义卡诺     

A Metal Nanoparticle Thermistor with the Beta Value of 10 000 K

The thermistor, typically made from metallic oxides, is a type of resistor whose electrical resistance is dependent on its temperature. Despite the wide usage, the limitations of ceramic thermistors become increasingly apparent as devices with improved performances are sought and as new applications emerge. Herein, a thermistor that is showed with a beta (B) value of 10 000 K can be made exclusively from metal nanoparticles functionalized with charged organic ligands. This B value is hard to achieve for ceramic devices, which is due to the increase of effective counterion concentration and its mobility upon thermal activation. Importantly, the performance of the nanoparticle thermistor is maintained when it is fabricated on a flexible substrate and experiences reversible bending. Demos of thermistor arrays for heat transfer, distribution, and comparison of their performance with commercial products are also demonstrated. Owing to the low temperature and simple casting process, conformably flexible characteristics, stable solid states, and ultra-high sensitivities, this device is expected to be practically used soon.     

Comparison of the Properties of Cu-Nb/Ti Composite Wires Fabricated by Wire Drawing and Swaging

This paper presents a comparison of the mechanical properties and microstructure of heavily deformed Cu-Nb/Ti composite wires produced via different fabrication routes. Three main fabrication routes; wire drawing, swaging and a combination of swaging and drawing, were employed with/without intermediate annealing heat treatments. Metallographic and mechanical testing techniques were used to characterize the wires. The experimental results showed that the wire produced by drawing exhibited the highest strength. Also, the application of intermediate heat treatment during fabrication resulted in the reduction of tensile strength. It was found that the strengthening of this high volume fraction Cu-Nb/Ti composite could not be explained by standard Hall-Petch type model.     

Abrasive Wear Characteristics of Carbon and Low Alloy Steels for Better Performance of Farm Implements

The low stress abrasion behaviours of heat treated mild, medium carbon and high C - low Cr steels, which are generally used in making farm implements, have been investigated. The simple heat treatment greatly improves the hardness, tensile strength and abrasion resistance of medium carbon and high C - low Cr steels. The results indicate that the material removal during abrasion is controlled by a number of factors, such as hardness, chemical composition, microstructure and heat treatment conditions. The conclusion is that the heat treated high C - low Cr steel and mild steel carburized by using coaltar pitch provide the best hardness and abrasion resistance and thus appear to be the most suitable materials for making agricultural tools.