Nano-B4C水基流体流变特性研究

对纳米流体粘度和流变特性的研究有助于揭示纳米流体强化传热和传质过程中的机理.选用纳米碳化硼作为纳米材料,研究了不同分散情况下纳米碳化硼流体的粘度值,通过粘度值来评价其流变特性.实验结果表明:不同种类分散剂、不同粒径纳米碳化硼对流体的流变性能影响较大;当pH值为6.8左右时溶液的粘度最小,溶液粘度随着温度的升高而显著降低;机械搅拌转速为650 r/min、超声波分散时间为10 min时溶液粘度分别有一个最佳值.     

喷嘴孔径对纳米流体强化氨水泡状吸收过程的影响

氨水吸收制冷系统取代压缩制冷系统在船舶上应用具有非常好的应用前景,而吸收性能的强化则有助于氨水吸收制冷系统性能的提高和整机体积的减少。本文针对纳米流体这种新型吸收强化方法开展研究。通过实验,分析了喷嘴孔径对纳米流体强化氨水泡状吸收过程的影响。研究结果显示,喷嘴孔径的变化不会恶化纳米流体的吸收强化效果,吸收强化比始终能够保持稳定。此研究结果将有助于纳米流体这种新型吸收工质在实际吸收制冷系统中的应用。     

B_4C陶瓷摩擦学性能研究现状与分析

碳化硼陶瓷以其独特的结构和性能广泛应用于诸多工业领域,其中作为一种耐磨或减磨材料,碳化硼陶瓷的摩擦学性能备受关注。总结了近年来国内外关于碳化硼陶瓷的摩擦学性能的研究报道,并从摩擦温度、负载、湿度、速度、磨程和配副材料等多种影响因素出发,讨论了碳化硼陶瓷的摩擦学特性。从实验结果可以看出,碳化硼陶瓷的摩擦学性能随实验条件的差异而出现较大范围的波动,摩擦因数在0.95～0.02之间。通过分析碳化硼陶瓷的摩擦与减磨机制,分析和讨论了碳化硼的摩擦学性能,并提出了改善其摩擦学性能的方法和建议。     

碳化硼材料研究进展

碳化硼陶瓷具有高硬度、高熔点和低密度的特点，是优异的结构陶瓷，在民用、宇航和军事等领域都得到了重要应用。研究了碳化硼结构陶瓷的优异性能和制备新工艺，综述了碳化硼材料的发展和研究现状，着重阐述了碳化硼陶瓷烧结的主要难点－致密化和韧化机理，提出利用原位自生法和前驱体热解法等新工艺制备纳米颗粒增强的碳化硼复合材料，是制备高性能碳化硼复合材料发展的新方向。     

Cu-水纳米流体对流换热特性研究

建立了测量纳米流体流动与对流换热性能的实验系统,探讨了不同pH值、分散剂浓度和纳米粒子质量分数对Cu-水纳米流体对流换热性能的影响。结果表明:pH值对Cu-水纳米流体对流换热系数的影响较小,这个现象启发了我们将纳米流体应用到未来工业中,可以不考虑pH值对纳米流体对流换热性能的影响。分散剂加入量是影响Cu-水纳米流体对流换热系数的重要因素,从分散稳定、导热系数和对流换热系数提高三个方面来考虑,在0.1%Cu-H2O纳米流体中,0.07%十二烷基苯磺酸钠被选为最优化浓度。另外,Cu-水纳米流体的对流换热系数随纳米粒子质量分数的增大而增大,但其对流换热系数的增加明显低于导热系数的增加。     

直接吸收式太阳能集热纳米流体光热特性研究

采用两步法配制了Co-H2O纳米流体,针对不同粒径、不同质量分数、不同pH值的纳米流体,与去离子水一起同步测试了其光热转换特性。实验结果表明:纳米流体的温升速率及集热量明显优于去离子水的。纳米流体质量分数有一最佳值,实验中质量分数为0.1%时效果最好,其最高温度要比纯水高出30.3%。30 nm Co-H2O纳米流体的光吸收能力要强于50 nm Co-H2O纳米流体的。pH值对光热特性有较大影响,实验中p H=8效果最佳。Co-H2O纳米流体优异的光吸收性能表明其有望运用在直接吸收式太阳能系统中。     

纳米流体强化对流换热的实验研究

建立了纳米流体对流换热系数的实验测试系统,利用实验系统测量YCu-H2O纳米流体的对流换热系数,探讨了纳米颗粒质最分数、Re数和轴向比对Cu-水纳米流体对流换热性能的影响.结果表明:Cu-水纳米流体的对流换热系数随纳米粒子质量分数的增人而增人,但其对流换热系数的增加明显低于导热系数的增加.随着雷诺数的增人,纳米流体的对流换热系数基本呈线性提高.纳米流体在实验管进口段的对流换热系数提岛值明显高于流体在充分发展段的提高值.纳米流体的导热系数、粘度和纳米颗粒迁移是影响纳米流体对流换热系数的主要因素.     

低温相变纳米流体释冷特性研究

在共晶盐BaCl2水溶液中悬浮粒径为20nm体积分数为1.13％的TiO2颗粒,通过添加分散剂和超声波振荡,制成分散均匀的TiO2-BaCl2-H2O纳米流体.对BaCl2溶液和纳米流体进行同步蓄冰放冷实验,实验表明:加入纳米TiO2粉体后,在融冰放冷时纳米流体融冰速率要比BaCl2溶液大,在同样时间内纳米流体放冷量要多于BaCl2溶液,在换热器中纳米流体总的传热系数要大于BaCl2溶液的,表明纳米粒子有助于强化蓄冷剂的传热性能.     

双组分纳米流体强化泡状吸收过程的实验研究

文章的主要目的是利用双组分纳米流体作为吸收工作介质来强化NH3/H2PO泡状吸收的过程。在实验中,配制了稳定的CNTs-ammonia双组分纳米流体,并利用泡状吸收实验装置进行了双组分纳米流体的泡状吸收实验。对颗粒的质量百分比和氨的初始浓度等因素对双组分纳米流体强化泡状吸收过程的影响进行了系统的实验研究,并分析了其强化机理。实验结果表明,CNTs-ammonia双组分纳米流体的吸收强化效果随着纳米碳管质量百分比的增加而先增加后下降,并且随着纳米流体中氨的初始浓度的增加而增加。     

基于纳米粒子/相变石蜡乳状液的研究

介绍了纳米流体的制备方法,探讨了纳米流体强化传热的机理.结合本实验室的研究方向,首次提出了在相变储热石蜡乳状液中添加纳米粒子强化石蜡乳状液传热性能的方法,并制备了纳米铝/石蜡乳状液.分析了该悬浮液的性能,实验结果表明,将0.1%(质量分数)的纳米铝粉分散于石蜡乳状液中,悬浮液的导热系数提高了29.4%,大大提高了石蜡乳状液的传热速率.与水作为储热、传热介质相比,该新型相变纳米流体具有储热密度大、换热能力强的优点.最后,指出了该新型相变纳米流体研究存在的问题并展望了其应用前景.     

Influence of coal tar pitch coating on the properties of micro and nano SiC incorporated carbon–ceramic composites

Carbon-micro or nano silicon carbide–boron carbide (C-micro or nanoSiC–B₄C) composites were prepared by heating the mixtures of green coke and carbon black as carbon source, boron carbide and silicon at temperature of 1,400 °C. Green coke reacts with silicon to give micron sized silicon carbide while the reaction between silicon and carbon black gives nano silicon carbide in the resulting carbon–ceramic composites. The green coke was coated with a suitable coal tar pitch material and used to develop carbon-(micro or nano) silicon carbide–boron carbide composites in a separate lot. The composites were characterized for various properties including oxidation resistance. It was observed that both types of composites made from uncoated as well as pitch-coated green coke exhibited good oxidation resistance at 800–1,200 °C. The density and bending strength of composites developed with pitch-coated green coke improved significantly due to the enhanced binding of the constituents by the pitch.     

Production and characterization of boron carbide and silicon carbide reinforced copper-nickel composites by powder metallurgy method

In this study, composite samples were produced by reinforcing boron carbide and silicon carbide particles in different rates by weight into copper-nickel powder mixture using powder metallurgy method. The prepared powder mixtures were cold pressed under 600 MPa pressure and pelletized. The pelletized samples were then sintered in an atmosphere-controlled furnace. Scanning electron microscopy to determine the microstructure of the produced samples and x-ray diffraction method analysis to determine the phases forming in the structure of the produced samples were used and microhardness was taken to determine the effect of boron carbide and silicon carbide on hardness. In addition to that, the mechanical properties the transverse rupture strength were investigated using three-point bending tests. The corrosion tests were performed potentiodynamic polarization curves of the samples in 3.5 % sodium chloride solution. The highest hardness value was measured as 162 HV 0.05 in the sample reinforced with 10 % boron carbide. As the amount of silicon carbide increased, the corrosion resistance of the composite increased. Moreover, as the amount of boron carbide increased, the corrosion resistance of the composite decreased. Load-contact depth values were examined, copper-nickel+10 % silicon carbide has the highest peak depth of 48.12.     

Influence of reinforcing particles on microstructure and mechanical properties of friction stir processed aluminium alloy AA7075-T651

This paper emphasis the improvement of mechanical properties of AA7075-T651 using friction stir processing through localized surface modification by adding nano boron carbide particles. The reinforcement techniques such as the groove and blind hole methods were used by changing reinforcements of nano boron carbide and a matrix of AA7075-T651 surface composites volume percentages (2 %, 4 %, and 6 %) along with tool rotational speed and processing speeds. Optical microscopy, scanning electron microscope and x-ray diffraction analysis were used to examine the particle dispersion for the surface composites and to correlate with the enhanced mechanical properties. Results revealed that high input parameters have given grain coarsening and precipitate agglomeration and low input parameters provide poor nugget metal consolidation and no vertical material flow. The L9 orthogonal Array designed and optimized the process parameters for enhancing the surface properties of processed samples. Mechanical properties like ultimate tensile strength, yield strength, hardness, percentage of elongation and impact strength were evaluated for the groove friction stir processing method and blind-hole friction stir processing methods. From the results, it has been observed that the blind-hole technique resulted in higher hardness and the homogenous dispersion of nano boron carbide particles in the stir zone than the groove method. Consequently, for blind-hole friction stir processing, grey relational analysis (GRA) and particle swarm optimization (PSO) approaches were proposed to optimise process parameters. From the compared optimization results between grey relational analysis and particle swarm optimization, particle swarm optimization approach was shown the best optimization results. Successively, the optimum condition in the respective experimentation is accomplished. Based on these observation and results, final validation tests were carried by changing the volume percentages of reinforcement keeping tool rotation speed and tool processing speed as constant. It is apparent that dynamic recrystallization in aluminium alloy at the processed zone due to presence of heterogeneous nucleation sites with nano boron carbide particles.     

Process and properties of electroless Ni–Cu–P–ZrO2 nanocomposite coatings

Electroless Ni–Cu–P–ZrO₂ composite coating was successfully obtained on low carbon steel matrix by electroless plating technique. Coatings with different compositions were obtained by varying copper as ternary metal and nano sized zirconium oxide particles so as to obtain elevated corrosion resistant Ni–P coating. Microstructure, crystal structure and composition of deposits were analyzed by SEM, EDX and XRD techniques. The corrosion behavior of the deposits was studied by anodic polarization, Tafel plots and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution. The ZrO₂ incorporated Ni–P coating showed higher corrosion resistance than plain Ni–P. The introduction of copper metal into Ni–P–ZrO₂ enhanced the protection ability against corrosion. The influence of copper metal and nanoparticles on microhardness of coatings was evaluated.     

On the structure and properties of wear- and corrosion-resistant nickel-chromium- tungsten-carbon-(silicon) alloys

In some applications, for chemical and physical reasons hard nickel-based alloys have to be used instead of cobalt-based alloys but boron must be avoided. The nickel-chromium-tungsten-carbon system with and without silicon was therefore studied in several concentration ranges at 1050°C with respect to structure, phase, hardness and corrosion and wear resistance. Alloys containing 2% carbon, 10% tungsten and more than 10% chromium are composed of a nickel solid solution and an M₇C₃ carbide in both cast and homogenized (1050°C, 180 h) conditions. On increasing the tungsten content up to 20% the M₂C carbide becomes dominant, and this is associated with a remarkable increase in the hardness of the alloys. Additions of 2% silicon do not change the M₇C₃ and M₂C carbides present. In some cases a carbon-stabilized silicide M₅Si(C) was observed. Silicon additions decrease the liquidus temperature range relatively little, but they affect particle shape and size and the grain size distribution. The relation of various chromium, tungsten and silicon contents to corrosion and wear resistance was studied. The corrosion resistance depends on the chromium content of the nickel solid solution but also on carbide formation (tungsten and carbon content). The silicon content of the nickel solid solution is important too.Because their liquidus temperature is close to 1300°C the alloys cannot be used as self-fluxing and fusing powders for flame spraying but they can be sprayed by plasma torches and they can, of course, be welded.     

Improvements of the microstructure and erosion resistance of boron carbide with additives

A series of test materials were produced from boron carbide (B₄C) powders with additions of either boron in amounts up to 60 wt.%, silicon (4 wt.%) or silicon and silicon carbide (4 wt.% and 30 wt.%, respectively). The powder mixtures were densified by encapsulation hot-isostatic pressing. The test materials where evaluated in dry particle erosion tests with silicon carbide grits. Particular attention was given to the relation between the microstructure and the composition.It was found that boron additions up to 20 wt.%, decreased the average grain size and reduced the porosity of the boron carbide. A material with 60 wt.% boron exhibited very low porosity and supreme resistance to particle erosion. The erosion resistance was also significantly improved by additions of silicon and silicon carbide.The favorable effects of boron, silicon and silicon carbide are discussed in terms of their influence on microstructural parameters, such as grain size, porosity, grain boundaries and reduction of free carbon.     

The influence of high-voltage electrical discharge on dispersion and structure of B<Subscript>4</Subscript>C powder

The influence of high-voltage electrical discharge on the distilled water–boron carbide powder dispersion system has been studied, making it possible to clarify the relationship between the discharge parameters and the powder dispersion and structure. It is shown that the necessary conditions for effective dispersion of the boron carbide powder are the compression wave pressure amplitude at least ca. 100 MPa and the specific processing energy about 20 MJ/kg.     

硼对铜合金组织和性能的影响

研究了加硼铜合金的组织以及力学、腐蚀、腐蚀磨损和冲蚀性能。结果表明：硼能明显细化铜合金的组织，提高其强度、硬度，改善其耐蚀、耐腐蚀磨损及耐冲蚀能力；并确定硼在铜合金中的最佳含量范围。     

Pressureless sintering and related reaction phenomena of Al2O3-doped B4C

The effects of alumina on the densification of boron carbide and related reaction phenomena in alumina-doped B₄C were studied. Pressureless sintering was conducted at various temperatures for 15 min in a flowing Ar atmosphere. The addition of alumina improved the densification of boron carbide. Maximum density of 96% theoretical was obtained with the 3 wt % alumina-doped B₄C sintered at 2150°C. Abnormal (or exaggerated) grain growth was observed in the specimen containing more than 4 wt % alumina. In the B₄C-Al₂O₃ reaction couples, good wetting of the liquid phase on the boron carbide grains was observed. X-ray diffraction and Auger electron spectra showed that the AlB₁₂C₂ phase was formed by the reaction between boron carbide and alumina. It is suggested that these phenomena promote the densification of boron carbide.     

Mechanical and thermal properties of HVOF sprayed Ni based alloys with carbide

The objective of the present study is to develop multi-functioned coating to the components, which are made of copper with electroplated Ni and are widely used for steel making industry. In this paper, we report the mechanical and thermal properties of Ni based superalloys with carbide sprayed by high velocity oxygen fuel (HVOF), and the detailed effects of sprayed material, spraying conditions, and initial powder structure on these properties. It was found that, among commercial Ni self-fluxing alloys (without fusing treatment), coating with a carbon content of 0.58 mass% had the most preferable properties, with a good balance of the hardness, strength, and thermal shock resistance. The thermal shock resistance depended not only on the strength of the coating but also on the volume contraction when tested at high temperatures. For the several developed Ni based superalloys with carbide, Ni20Cr8Mo5Fe–WC and Ni16Cr15Mo3–WC demonstrated the prominent adhesion strength and thermal shock resistance with high Galvanic corrosion resistance through optimized spraying condition. Also, 20 mass% NiCr–Cr₃C₂ coating sprayed by using employed relatively small primary particle succeeded in achieving the multi-superior properties; high adhesion strength, high corrosion resistance and thermal shock resistance.