基于气体捕捉法的泡沫Ti-6Al-4V等温发泡规律研究

为了确定气体捕捉法制备泡沫Ti-6Al-4V等温发泡过程中孔隙率和微观孔洞的变化规律,在不同发泡温度及发泡时间下制备了泡沫Ti-6Al-4V.运用阿基米德原理对泡沫Ti-6Al-4V的孔隙率进行测量,通过OM和SEM对其微观特征进行观察.研究表明:泡沫Ti-6Al-4V的孔隙率及孔径均随等温发泡温度升高而增加;但当发泡温度大于950℃时,孔隙率和孔径均减小,且孔洞形态由球形变成多边形,这是由于基体内生成大尺寸β相造成的.增加发泡时间能以促进孔洞长大的方式提高泡沫Ti-6Al-4V的孔隙率,球形孔洞数量随着发泡时间的增加逐渐增多.经950℃/10 h发泡得到了孔隙率34.2%、孔径平均值156μm、孔洞为球形且分布弥散的泡沫Ti-6Al-4V.     

封面图片说明

<正>封面图片出自论文"基于气体捕捉法的泡沫Ti-6Al-4V等温发泡规律研究"。为了确定等温发泡温度对泡沫Ti-6Al-4V孔洞状态的影响规律,进行了不同温度的等温发泡试验。这幅图片为经950℃/50 h等温发泡制备的泡沫Ti-6Al-4V(孔隙率为34.8%)孔洞状态扫描电子显微镜照     

氢辅助气体捕捉法制备泡沫Ti-6Al-4V及其机理研究

对气体捕捉法制备泡沫Ti-6Al-4V过程中未发泡的坯料进行置氢处理,然后再进行等温发泡。运用阿基米德原理对发泡后坯料孔隙率进行测量。通过OM和SEM对坯料内部微观特征进行观察。研究氢对坯料等温发泡过程的影响规律及作用机制。结果表明:质量分数为0.15%的氢能将坯料最佳发泡温度降低60℃,即在890℃下孔隙率可达到32.88%(体积分数),孔径达到160μm,孔洞分布弥散的泡沫Ti-6Al-4V。主要机理:氢以降低坯料(α+β)/β相转变温度的方式,提高基体内塑性较好的β相比例,并能在一定程度上软化α相,降低坯料高温流变应力,进而降低最佳发泡温度。     

泡沫铝合金三明治结构结合界面及剪切性能的研究

提出了一种新的泡沫铝合金三明治结构的制备工艺--直接将铝板/混合粉末/铝板通过一次大压下量复合轧制,然后在炉中直接发泡成最终产品的制备工艺.实验成功的制备出铝面板的泡沫铝合金芯的三明治板.讨论了铝面板泡沫铝夹芯板轧制过程中以及发泡过程中界面的结合情况及界面结合机理.结果表明,轧制过程中界面结合属于机械结合,结合机制为薄膜理论;发泡过程中界面结合属于冶金结合,而铝面板与粉末体结合发泡后,界面处则只发生Al原子的互扩散,没有新相生成.剪切实验结果表明,预制坯的界面剪切强度较低,能够直接在界面处剥离开或者将板剥离开一半后将板拉断;而发泡后的泡沫铝夹芯板的界面结合力很强,剪切时断裂发生在芯材中或者铝面板上.     

搅拌摩擦焊制备7075铝合金泡沫夹芯板塑性变形及发泡工艺研究

目的 研究搅拌摩擦焊(FSW)制备泡沫铝夹芯板(AFS)预制坯的成形规律和发泡过程中泡孔的演变规律。方法 采用搅拌摩擦焊工艺制备7075铝合金泡沫夹芯板。利用金相显微镜和扫描电子显微镜对不同焊接参数条件下AFS预制坯组织形貌进行分析,同时,利用单向拉伸和高温杯突试验对不同温度下AFS预制坯的成形性能进行研究,并且针对AFS预制坯发泡性能及不均匀热变形行为对发泡性能的影响进行分析。结果 在焊接转速为2 000 r/min、进给速度为50 mm/min情况下,可获得板粉混合均匀、无明显缺陷的接头;在450 ℃时,搅拌摩擦焊制备的预制体与轧制板材的成形性能相似,真应变达到0.55,伸长率高达73%。450 ℃下杯突试验样品再结晶比例从60.6%增加至82.7%。在680 ℃发泡温度下,保温225 s,能够制备孔径结构均匀、高质量的铝合金泡沫夹芯板。结论 搅拌摩擦焊工艺制备的预制坯经过塑性变形后进行发泡,可以获得具有均匀孔隙结构的泡沫夹芯板弯曲部件。     

泡沫铝夹心板芯层泡沫结构的研究

研究了采用轧制复合-粉末冶金发泡法制备的泡沫铝夹心板的生产工艺,探讨了主要工艺条件对芯层泡沫结构的影响,得到了优化的工艺参数.研究结果表明:轧制复合工艺可以使芯层粉末达到很高的致密度,为发泡过程创造了有利条件.轧制复合板适宜的发泡温度为615～620℃,温度过高会导致芯层出现大尺寸连通孔.发泡时间对熔融态泡沫体的凝固过程有显著影响,时间过长会使泡沫层塌陷,发泡温度为620℃时,经4～6min发泡芯层可形成良好的泡沫结构.     

脉冲电流对0.27%置氢Ti-6Al-4V合金变形行为的影响

对0.27%(质量分数)置氢Ti-6Al-4V合金进行压缩试验,对断口进行观察与分析,研究了脉冲电流对其变形行为的影响。结果表明,脉冲电流使0.27%置氢和未置氢Ti-6Al-4V合金的变形抗力降低和压缩延伸率提高。脉冲电流产生的焦耳热效应,是影响0.27%置氢Ti-6Al-4V合金力学性能变化的主要原因。由于电致塑性效应的影响,Ti-6Al-4V合金的断裂形式由延性脆性沿晶断裂向准解理穿晶断裂转变,但是对于0.27%置氢Ti-6Al-4V合金,由于在低温条件下氢脆的影响其准解理断裂特征不如未置氢Ti-6Al-4V合金的明显。     

TC4钛合金板不同加工条件下组织对比研究

通过对Ti-6Al-4V钛合金进行常规锻造及换向墩拔锻造热塑性变形加工,然后再进行多火次换向热轧变形,研究换向墩拔锻造热塑性变形加工及多火次换向热轧变形过程中Ti-6Al-4V钛合金组织的演变。试验结果表明,采用墩拔锻造与多火次轧制加工方式,板坯组织由原始双态组织(等轴α及转变(α+β))逐步演变成完全等轴α组织形态,组织更加细小、均匀,有效保证了板材组织及性能各向同性。     

泡沫铝夹心板的制备及其界面结合机理的研究

由泡沫铝芯材与金属面板构成的夹心结构具有轻质、高强度、良好的减震性等优点.现存的泡沫铝夹心板的制备方法很多,但均为先制备芯材再进行连接的方法.本研究提出一种新的工艺方法即采用粉末与面板直接轧制然后发泡的方法制备了Fe/Al/Fe泡沫铝夹心结构.研究了泡沫铝芯的发泡不均的问题,分析了发泡前和发泡后面板与泡沫铝芯的冶金结合过程,提出了扩散微观结合机理.最终面板与泡沫芯材通过扩散反应形成了牢固的冶金结合.     

Ti及Ti-6Al-4V的水基凝胶注模成形研究

将凝胶注模工艺应用于金属Ti及Ti-6Al-4V合金粉末的坯体成形,研究了高固相含量的Ti粉和Ti-6Al-4V合金粉末的料浆的制备.结果表明,用凝胶注模工艺制备出了固相含量为54ψ%的钛合金粉末料浆和形状复杂的坯体;粉末的颗粒形状是影响料浆固相含量的重要因素,球形粉末配制成的浆料固相含量最高,近球形次之,片状最低;分散剂柠檬酸铵也可以显著提高浆料的固相含量.     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.