激光区熔定向凝固Al2O3/Y3Al5O12 (YAG)共晶的组织与断裂韧性

采用激光区熔高温度梯度快速定向凝固技术从熔体中直接制备Al2O3/Y3Al5O12(YAG)共晶自生复合陶瓷,以研究其在超高温度梯度(1.0×106 K/m)下的快速凝固组织特征及与激光工艺参数的关系,并对其力学性质进行分析.研究结果表明:凝固组织强烈地受激光扫描速度与功率密度的影响,当二者匹配时,Al2O3相和Y3Al5O12(YAG)相呈现均匀一致,连续分布的层状耦合共晶结构,共晶间距细小(1～2 μm),且随扫描速度的增大逐渐减小;所制备的Al2O3/Y3Al5O12(YAG)共晶陶瓷硬度高达19.5 GPa,断裂韧性达到3.6 MPa·m1/2.     

纳米Al2O3的晶型对聚酰亚胺杂化薄膜性能的影响

将经偶联剂处理的纳米Al2O3粉体,借助超声波以一定方式均匀分散于聚酰胺酸溶液中,制备出Al2O3不同晶型、不同含量的PI/纳米Al2O3杂化薄膜,并对杂化薄膜微观形貌、聚集态结构、光透过率、热稳定性、电击穿场强进行研究,分析Al2O3晶型和含量对PI/纳米Al2O3杂化薄膜的结构和性能的影响.结果表明:PI/纳米Al2O3杂化薄膜的热稳定性,电击穿场强均高于纯PI薄膜,且随着纳米Al2O3含量的提高热稳定性也随之提高,电击穿场强先升高后降低;填充Al2O3粉体的晶型对PI薄膜分子链堆积密度有较大的影响,导致添加不同晶型Al2O3的杂化薄膜性能的差异.     

纳米Al2O3对聚酰亚胺复合薄膜导热性能的影响

选用两种不同纳米氧化铝粉体,采用直接掺杂法制备不同含量纳米氧化铝/聚酰亚胺复合薄膜.研究复合薄膜的导热系数与无机含量的关系,探讨纳米氧化铝粉体种类对复合薄膜导热性能的影响.结果表明:同一温度下,复合薄膜的导热系数随Al2O3含量的增加而增大;当纳米氧化铝含量小于15%(质量分数)时,选用亲水性纳米Al2O3粉体的复合薄膜导热性能比选用亲油性的复合薄膜的好;当纳米氧化铝的加入量为5%时,复合薄膜的强度和韧性均有明显增加;亲水性纳米氧化铝加入量为5%～10%时,复合薄膜的导热性能提高并能保持一定的力学性能.     

SHS—快速加压合成TiC,Al2O3／Al复合材料的工艺研究

利用SHS反应－快速加压的方法制备了Al2O3,TiC/Al复合材料,研究了在不同Al,Al2O3加入条件下燃烧反应的特征及制备的Al2O3,TiC/Al复合材料的相,组织特征,发现一定过量Al的存在对材料的致密化作用明显,在过量w(Al)为10％时,获得的材料相对密度达到97．5％,抗弯强度提高约20％。     

超重力下燃烧合成Al2O3-ZrO2(Y2O3)共晶陶瓷组织性能演化

采用超重力下燃烧合成工艺进行Al2O3-ZrO2 (4Y)共品陶瓷的制备,研究了Al2O3-ZrO2(4Y)共晶陶瓷的凝固行为、组织演化与力学性能的关系.XRD、SEM与EDS分析显示陶瓷基体组织是由表层的微纳米晶组织和心部的ZrO2四方相微米球品组织组成.陶瓷表层微纳米品组织的形成是因Al2O3高熵相率先形核和Al2O3各向异性生长,诱发Al2O3-ZrO2(4Y)小平面-小平面共晶生长所致;处于陶瓷心部的ZrO2四方相微米球晶组织则是因ZrO2高温立方相快速生长,导致Al2O3和ZrO2独立长大所致.力学性能测试结果表明因陶瓷凝固行为引起的显微组织演化,使其表层具有最大的维氏硬度(20.2GPa),而其心部则具有最高的断裂韧性(18.5±1.6MPa·m1/2),陶瓷弯曲强度达至1268±112MPa.     

化学沉淀法制备纳米氧化铝过程中的防团聚研究

分别以无水乙醇、去离子水为溶剂,以NH3·H2O、NH4HCO3为沉淀剂,采用化学沉淀法制备了纳米Al2O3粉体.利用TEM、XRD、FT-IR和激光粒度仪研究了溶剂、沉淀剂、浓度、前驱体等因素对纳米Al2O3粉体制备过程中的团聚程度的影响.结果表明:当NH4HCO3和Al(NO3)3水溶液浓度分别为3.0mol/L和0.3mol/L时,借助超声分散和微波干燥,得到的纳米Al2O3粉体粒度均匀、分散良好,1100℃煅烧所得粉体平均粒径为20nm.     

管状阳极氧化铝模板的表面氧化应力分析及其应用研究

通过对高纯铝片预制铝管分别进行"外表面阳极氧化"(外氧化)和"内表面阳极氧化"(内氧化)制备了管状多孔氧化铝模板(AAO),考察了氧化过程中Al/Al2O3界面的应力影响。实验直观表明,"外氧化"过程中Al/Al2O3界面产生拉伸应力易导致管状模板产生轴向裂纹;而"内氧化"过程中Al/Al2O3界面产生压缩应力使管状模板更加紧密而不易破裂。研究结果表明,Al/Al2O3界面上拉伸应力的有效释放是获得无裂纹管状阳极氧化铝模板的关键。最后,利用管状氧化铝模板制备了放射状Cu纳米线阵列,并对其在膜渗透方面的应用进行了初步尝试。     

包覆型α-Al_2O_3粉体的制备及表征

以平均粒径为22μm和0.5μm的α-Al2O3粉体为起始原料(以下分别简称Al2O3(C)和Al2O3(F)),分别以聚乙烯亚胺(PEI)和聚甲基丙烯酸铵(APMA)为聚合物电解质,采用非均相凝固法将Al2O3(F)颗粒均匀地包覆在Al2O3(C)粉体表面.重点考察了聚合物电解质的吸附时间、Al2O3(C)/Al2O3(F)的质量比、两种分子量的PEI对包覆型氧化铝粉体制备的影响.当Al2O3(C)/Al2O3(F)的质量比为1∶3,经过分子量约为60 000的PEI处理2 h的Al2O3(C)粉体表面均匀地包覆了Al2O3(F)颗粒(经APMA处理2 h).采用该包覆型粉体制备出片状多孔支撑体,其孔隙率为35.8%,平均孔径为2.9μm,纯水通量为205 m3/(m2.h.MPa).     

改进的Sol-gel法制备Ba0.6 Sr0.4 TiO3厚膜

采用Sol-gel法在Pt/Ti/SiO2/Si和Al2O3基片上制备厚度为2～14μm的Ba0.6Sr0.4TiO3(BST)铁电厚膜材料.经高能球磨细化和表面改性后的BST陶瓷纳米粉体分散到BST溶胶中,通过甩胶法,形成0-3型BST厚膜材料.XRD图谱显示,BST呈现纯钙钛矿相结构;SEM照片显示,BST厚膜均匀致密、无裂纹;介电性能测试结果表明,当测试频率为1kHz,温度为25℃时,介电常数为620,介电损耗为0.6.     

溶胶-凝胶法制备聚酰亚胺/Al2O3纳米复合材料的研究

采用溶胶-凝胶法制备了聚酰亚胺(PI)/Al2O3纳米复合薄膜,通过测定胶液在贮存过程中粘度的变化研究了纳米复合胶液的贮存稳定性,采用热失重分析、拉伸强度和体积电阻率等测试方法研究了纳米复合薄膜的性能.结果表明,当Al2O3含量不大于14%时,纳米Al2O3前驱体的存在对纳米复合胶液的贮存稳定性影响不大或基本上没有影响;与纯PI薄膜相比,Al2O3含量不大于5%时,纳米复合薄膜的表观分解温度、拉伸强度以及常态下的体积电阻率均有明显提高;纳米Al2O3的存在有利于改善薄膜的高温电性能.     

表面处理对第二代单晶高温合金胞状再结晶的影响

对第二代镍基单晶高温合金进行表面处理并在1000～1200℃保温,研究表面加工工艺和热处理条件对胞状再结晶行为的影响.结果表明:磨削、吹砂、喷丸试样热处理后表面均发生了胞状再结晶,其生成厚度依次增加.喷丸试样经1200℃/50h后胞状再结晶区厚度可达0.1mm,晶团之间及与基体之间存在取向差小于5°的小角晶界和35～4...     

生产技术的虚拟世界

对虚拟现实的方法及专用工具作了概述,重点放在一般技术现状以及生产技术的特别潜能,并以磨削刀具为例介绍了虚拟现实的应用。     

New Vitrified Bond Diamond Grinding Wheel for Grinding the Cylinder of Polycrystalline Diamond Compacts

In this work, a kind of new vitrified bond based on Li2O-Al2O3-SiO2 glass ceramics was used to bond the diamond grains, which is made into grinding wheel and the cylindrical grinding process of polycrystalline diamond compacts （PDCs） by using the new vitrified bond diamond grinding wheel was discussed. Several factors which influence the properties of grinding wheel such as amount of vitrified bond and the kinds and amount of stuff in grinding wheel were also investigated. It was found that the new vitrified bond can firmly combine diamond grains, when there are only diamonds and vitrified bond in the structure of grinding wheel, the longevity of the grinding wheel is about 2.5-3 times as that of resin bond grinding wheel for processing PDCs. The grinding size precision of PDCs can be improved from 4-0.03 mm to 4-0.01 mm because of larger Young＇s modulus of vitrified bond than resin bond. The grinding time of a PDC product can be 1.75-2.0 min from 3.25-3.5 min, so this kind of grinding wheel can save much time for processing PDCs. Also, there is hardly noise when using this new vitrified bond diamond grinding wheel to process PDCs. The amount of vitrified bond in grinding wheel influences the longevity of grinding wheel. When the size of diamond grains is 90-107 μm, the optimal amount of vitrified bond in grinding wheel is 21% （wt pct）. When the amount of vitrified bond exceeds 21%, there are many pores in grinding block, which will decrease the longevity of grinding wheel. The existence of addition stuff such as Al2O3 or SiC can reduce the longevity of grinding wheel.     

Development of a miniature cryogenic fluid circuit and a cryogenic micropump

This article presents the development of a miniaturized cryogenic fluid circuit for distributed cooling of low-temperature tracking detectors in high-energy physics (HEP). The heart of the circuit is a prototype cryogenic micropump. This volumetric pump is compatible with cooling powers of about 10-100 W, and capable of producing pressure heads of up to around 0.3 MPa. Besides detector and electronics cooling in HEP, potential applications are found in the field of superconductor technology.     

基于VMD-PNN的砂轮钝化声发射检测

在磨削加工过程中,加工刀具即砂轮会发生钝化现象,砂轮表面磨损影响加工精度和工件质量,需要及时检测并修整。磨粒的塑性变形、破碎、断裂等会产生声发射信号,能够作为精确识别砂轮钝化状态的依据,且不易被噪声干扰,因此提出一种基于变分模态分解（Variational Mode Decomposition,VMD）和概率神经网络（Probabilistic Neural Network,PNN）的砂轮钝化声发射检测方法。VMD可以将原始信号分解为多个本征模态函数（Intrinsic Mode Function,IMF）分量,筛选其中峭度较大的分量重构即得到声发射信号。声发射检测的关键是特征参数的选取,在相关研究基础上本文提出了声发射包络能量占比作为一个重要的特征参数,并选取了共5种特征参数,构建出5维特征向量数据集,输入到PNN中进行训练,经过测试识别准确度达到94.5%。该方法建立了声发射信号特征参数与砂轮不同钝化状态的关系,能够对砂轮严重钝化状态给出准确预警,具有实际应用价值。文章比较了声发射信号不同特征参数用于识别砂轮钝化状态的准确度,对特征参数的选用具有参考意义。     

滚轮体表面裂纹成因分析

某20CrMnMo钢滚轮体渗碳、淬火后进行磨削时表面发现裂纹,通过对其进行宏观检验、化学成分分析、非金属夹杂物检验以及金相检验,对裂纹产生原因进行了分析。结果表明:该滚轮体表面裂纹属于磨削裂纹;主要是由于刀刃砂粒的不平整以及磨削工艺的不合理导致的。通过改进磨削工艺较好地解决了滚轮体磨削裂纹产生的问题。     

Operation of a TES microcalorimeter cooled by a compact liquid-helium-free He-He dilution refrigerator directly coupled to a Gifford-McMahon cooler

A superconducting transition edge thermosensor (TES) microcalorimeter was irradiated with LX-ray photons emitted by an ²⁴¹Am source maintained at an operating temperature of 120 mK using a compact liquid-helium-free ³He-⁴He dilution refrigerator directly coupled to a Gifford-McMahon (GM) cooler. The first and second stages of the GM cooler were directly coupled to the first and second pre-cool heat exchangers of a stick shaped dilution unit through copper plates in a vacuum chamber. The helium-free dilution refrigerator provided a cooling power of 20 μW at 100 mK. Detection signals of LX-ray photons emitted by the ²⁴¹Am source were observed by operating the TES microcalorimeter in a severe noise environment induced by the mechanical vibrations of the GM cooler.     

新型往复式抛光机磨头创新设计及动力学分析

为了研究大规格瓷砖加工设备,提出一种新型往复式抛光机磨头。从结构原理上继承了摆动式抛光磨头的优势,弥补了存在的缺陷,达到了加工大规格瓷砖的要求。以新型往复式抛光磨头磨块座系统为研究对象,建立力学和动力学模型。得出磨块座系统中动点的运动轨迹是沿着y方向的直线运动,同时分析得出磨块质量小于其他（除磨块以外）质量可以保证新型磨头的结构稳定性。     

Cryogenic propellant liquefaction and storage for a precursor to a human Mars mission

An analysis of cryogenic liquefaction and storage methods for in-situ produced propellants (oxygen and methane) on Mars is presented. The application is to a subscale precursor sample return mission, intended to demonstrate critical cryogenic technologies prior to a human mission. A heat transfer analysis is included, resulting in predicted cryogenic tank surface temperatures and heat leak values for different conditions. Insulation thickness is traded off against cryocooler capacity to find optimum combinations for various insulation configurations, including multilayer insulation and microspheres. Microsphere insulation is shown to have promise, and further development is recommended.     

Accidental release of hydrogen from a cryogenic tank

Liquid hydrogen at 20 K was harmlessly released at Turin’s Porta Susa station over a period of seven hours on 9 July 1991 through the safety valve of a dewar-type tank on a railway wagon following the loss of the vacuum between its two walls. Commercially available programs were unable to model this type of release in the unusual conditions in which this hydrogen had been stored. A model illustrating the course of the accident was therefore worked out. A start was made by examining the changes in the physical and thermodynamic properties of the hydrogen progress in the dewar to find out how long it had taken to build up the pressure needed to open the safety valve.Owing to the complex geometry of the insulating layer in the interspace of the dewar on which the liquefaction of the air took place, the heat exchange coefficient could not be determined a priori. It was therefore assumed and subsequently quantified by means of an iterative process. The thermodynamic data were then used to examine the outflow of the hydrogen from the venting line. Flow dynamic calculations showed that the hydrogen was entirely lost through the safety valve and that pressure losses along the approx. 3-m line were negligible. The model also showed that the speed of the outflow was subsonic. The speed evaluated will enable the dispersion of the hydrogen and hence the areas at risk to be evaluated in the subsequent stages of the study.