组分对Ti3SiC2/Cu复合材料性能的影响

用热压法制备出Ti3SiC2/Cu复合材料,对复合材料的密度、弯曲强度和电阻率进行测试,并研究了组分对材料性能影响.研究结果表明,在复合材料中Ti3SiC2体积分数为50％～70％的实验范围内,不同组分的复合材料具有不同的最佳烧结温度,烧结温度过高时会对材料性能产生不利影响.相同工艺参数下,随着铜含量的增加,复合材料的弯曲强度升高、电阻率降低.提高致密度可在提高复合材料抗弯强度的同时降低材料的电阻率.     

微波烧结多孔β-TCP/HA双相生物陶瓷的性能

用微波烧结法制备出多孔β-TCP/HA双相生物陶瓷,研究了烧结温度、烧结时间及加热速度对生物陶瓷性能的影响.优化烧结工艺后,得到了平均晶粒尺寸约400 nm,气孔率约48%,强度为1.10 MPa的多孔β-TCP/HA双相陶瓷.用微波烧结方法可以制备出良好的多孔β-TCP/HA双相生物陶瓷,其线收缩率和抗压强度随着烧结温度的升高和烧结时间的延长而增大.与常规马弗炉烧结相比,在多孔β-TCP/HA双相生物陶瓷的线收缩率和抗压强度相同的情况下,微波烧结温度降低了大约100℃,提高了烧结效率,降低了能耗.微波烧结钙磷生物陶瓷具有更好的生物活性.     

不同矿化剂对铝基陶瓷型芯性能的影响

研究了在不同烧结温度下不同矿化剂对氧化铝基陶瓷型芯性能的影响,通过收缩率、室温抗弯强度、高温挠度的测试以及XRD和SEM分析表明:烧结温度为1250～1450℃时,同样粒度配比的两种型芯收缩率均随烧结温度的升高而逐渐增大;随着烧结温度的升高只添加氧化硅的型芯的室温抗弯强度呈先升高后降低的趋势,在1400℃时达最大值,只添加氧化钇的型芯的室温抗弯强度则随烧结温度的升高不断增大;随着温度的升高,只添加氧化硅的型芯的高温挠度逐渐减小,而只添加氧化钇的型芯虽有少许钇铝石榴石生成,但其高温挠度仍很大,只出现了少许的波动。因此只添加氧化硅的型芯性能优于只添加氧化钇的型芯的性能。     

表面改性碳纤维增强羟基磷灰石复合材料抗弯性能的研究

通过在碳纤维表面原位生成莫来石保护层和对氨基苯甲酸表面处理来改性碳纤维,将改性碳纤维与羟基磷灰石(HA)复合,制备表面改性碳纤维增强HA复合材料。研究改性前后的碳纤维对复合材料抗弯强度的影响并分析增强机理。结果表明,随纤维含量的增加复合材料的抗弯强度先提高后下降,碳纤维含量为3%(体积分数)时复合材料的抗弯强度达到最大值。碳纤维、表面处理碳纤维、表面复合处理碳纤维增强HA材料的抗弯强度均随烧结温度的升高而提高,且整体提高幅度依次增大,当烧结温度达1150℃时,3种材料的抗弯强度达最大值,分别为55.13、100.95、112.17MPa。表面复合处理碳纤维增强HA材料的抗弯强度比基体提高最多为3.5倍。这主要归因于碳纤维表面通过原位反应形成莫来石3Al2O3.2SiO2保护层,同时经对氨基苯甲酸处理后碳纤维对HA有更好的亲和性和吸附性。     

烧结温度对莫来石增强磷酸铬铝材料的制备与性能影响

以固相烧结莫来石为增强体,制备了莫来石增强磷酸铬铝基复合材料。研究了烧结温度对复合材料的微观结构和性能的影响。采用SEM、XRD、EDS等检测手段对复合材料的物相结构及断面的微观形貌进行分析,使用万能试验机测试其材料的抗折强度,并使用矢量网络分析仪分析材料的介电性能。结果表明,随着烧结温度的升高,复合材料中莫来石的晶粒依次增大,材料致密度、介电常数增加,抗弯强度增加,但过高的烧结温度下抗弯强度会降低。当烧结温度为1 500℃时,材料的抗弯强度为107 MPa,平均介电常数为3.57。     

梯度多孔Mg-Ca合金的力学性能研究

主要研究了具有不同孔隙梯度分布的多孔Mg-Ca合金在横向和纵向压缩时孔洞的受力以及变形特征,分析了梯度多孔Mg-Ca合金在弯曲时裂纹扩展机理,并观察了孔隙梯度结构和烧结温度对梯度多孔Mg-Ca合金力学性能的影响。研究结果表明,梯度多孔Mg-Ca合金的力学性能优于均匀多孔材料,随着试样边缘和中心孔隙度差距的增加,试样的抗弯强度、抗压强度和弹性模量均增加,纵向压缩时样品抗压强度和弹性模量的增加优于横向压缩,这主要归因于孔隙的梯度分布导致受力时外加载荷的重新分配。随着烧结温度增加,梯度多孔Mg-Ca合金的力学性能增加,在620℃烧结2h时力学性能达到最佳。     

热固性硅树脂压注法制备多孔硅基陶瓷型芯研究

以石英玻璃粉为基体, 热固性硅树脂为增塑剂, 利用压注方法制备了多孔硅基陶瓷型芯, 研究了烧结温度和保温时间对样品性能的影响。研究结果表明: 随着烧结温度的升高, 反玻璃化进程加快, 在烧结温度1250℃, 随着保温时间的延长, 玻璃相发生了转变, 逐渐析出方石英, 且含量不断增加; 样品的线收缩率和失重随烧结温度的升高略微增加, 但烧结时间的影响较小。样品的失重主要是由于硅树脂的分解引起的。在1250℃烧结10 h后, 得到样品的收缩率为0.93%, 显气孔率为32.8%, 抗弯强度为9.08 MPa。     

凝胶注模成型技术制备氧化石墨烯/HA复合材料的研究

以氧化石墨烯和纳米羟基磷灰石(HA)粉体为原料,采用凝胶注模成型技术制备了氧化石墨烯/HA复合材料。研究了有机单体、浆料固相含量和石墨烯含量对氧化石墨烯/HA浆料粘度的影响,观察了陶瓷浆料的凝胶固化过程并测量了固化后生坯的密度和抗压强度,分析了氧化石墨烯含量对烧结后复合材料抗弯强度和断裂韧性的影响,观察了试样断口的显微组织。研究结果表明,有机单体含量为15%(质量分数,下同),固相含量为45%,氧化石墨烯含量为1.5%时,氧化石墨烯/HA浆料的粘度最佳,为362.9mPa·s,浆料的分散性良好,固化后生坯具有较高的密度和抗压强度。随氧化石墨烯含量的增加,复合材料的抗弯强度和断裂韧度均先增加后降低。当氧化石墨烯含量为1.5%时,1 150℃烧结样品的抗弯强度为81.5MPa,断裂韧性为1.52MPa·m1/2,分别比HA基体提高了151.8%和74.7%,因此添加氧化石墨烯后的HA复合材料的力学性能更佳。     

钼铜复合粉末的致密化及性能

对微波辅助法制备的钼铜复合粉末进行压制烧结,研究其致密化行为及复合材料性能。结果表明:烧结温度是控制钼铜复合材料成分、微观组织及综合性能的关键因素。1100℃下烧结的钼铜复合材料Cu含量最接近设计含量,过高的烧结温度将引起铜的损耗。在较低的烧结温度下(≤1100℃),复合材料的力学性能和物理性能随温度的升高而升高,但是过高的烧结温度(1200℃)会引起铜相的大量损失及颗粒异常长大,从而导致复合材料密度、硬度、导电率及导热率的降低。通过优化实验参数,1100℃下的复合材料具有理想的微观结构,铜相损失较少,复合材料成分接近设计成分,钼铜两相分散较为均匀,力学性能及物理性能优异,复合材料的密度、硬度、抗弯强度、电导率及热导率分别为9.79g/cm^3,229.1HV,837.76MPa,24.97×10~6S·m^-1和176.57W·m^-1·K^-1。     

烧结温度对反应热压烧结制备ZrB2-ZrC-W2Zr复合材料组织和力学性能的影响

以B_4C、Zr、W为原料,采用反应热压烧结工艺制备了ZrB_2-ZrC-W_2Zr复合材料,系统研究了烧结温度对复合材料组织结构和力学性能的影响规律。结果表明,复合材料主要由ZrB_2、ZrC、W_2Zr和少量的W组成,随着烧结温度从1 600℃升高到1 900℃,W的含量略有增加,W_2Zr的含量略有减少,ZrB_2晶粒的形态由针状向板条状转变,晶粒尺寸逐渐增大,而长径比逐渐减小。复合材料的抗弯强度和断裂韧性随着烧结温度的升高先增大后减小,在1 850℃出现峰值,分别达到约560 MPa和5.5 MPa·m~(1/2)。     

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.     

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.……     

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.     

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...     

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.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

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.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...