Cr2AlC陶瓷的制备及性能

以铬粉，铝粉和石墨为原料，采用热压方法制备Cr2AlC陶瓷材料．研究了组成、烧结温度对试样物相和密度的影响．研究结果表明，当原始组分中Al过量低于20at％时，样品中的主相为Cr2AlC，另有微量的Cr7C3相．Al过量超过20at％时，样品为Cr2AlC单相．试样的块体密度随Al过量的增大而下降．Al过量10at％在1400℃热压1h试样的室温硬度、弯曲强度和杨氏模量分别为3．5GPa，375MPa和278GPa．在75-269K温度区间，样品的电导率随温度增加而线性地减少，具有金属特性．文中还报道了样品的热学性能．     

热压反应烧结法制备Al_2O_3/Ti_2AlC复合材料及其微观结构和性能

以Ti、Al和活性炭粉为原料,通过高能球磨及热压反应烧结法在1200℃合成Al2O3/Ti2AlC复合材料,即是在Ti2AlC层状材料的制备过程中同时被合成。研究了烧结温度对反应产物的影响,并重点分析了材料微观结构和性能的关系。结果表明:高能球磨使Ti2AlC的烧结温度降低,热压烧结在1200℃时得到了物相比较均匀、致密的Al2O3/Ti2AlC复合材料;同时分析材料微观结构,少量Al2O3的引入抑制了Ti2A1C晶体的异常长大,使得晶粒细小且均匀。力学性能测试表明,该材料室温抗弯强度可达275.4MPa,断裂韧度可达10.5MPa.m1/2,密度为4.2g/cm3。     

原位热压TiC/Ti/Al合成Ti2AlC的研究

以TiC/Ti/Al为原料,采用热压工艺在1400℃原位合成和烧结了含少量第二相Ti3AlC2的Ti2AlC材料.通过不同温度和不同热压时间下合成试样的XRD分析探讨了Ti2AlC的合成过程.结果表明,高温下Ti与Al反应生成中间相TiAl金属间化合物,然后TiC与TiAl金属间化合物反应生成Ti2AlC.初期反应非常迅速,大部分Ti2AlC在此阶段生成.反应后期反应物减少,速度变慢,同时生成少量第二相Ti3AlC2.不同温度下合成的Ti2AlC颗粒具有不同的形貌特征.     

Cr_2AlC陶瓷的合成及其摩擦磨损性能

以Cr粉、Al粉和石墨为原料,采用热压原位反应烧结合成Cr_2AlC陶瓷材料。研究不同的烧结温度对合成Cr_2AlC陶瓷的物相组成和性能的影响,对Cr_2AlC陶瓷的摩擦磨损性能进行了测试研究。实验结果表明,按照摩尔比n(Cr)∶n(Al)∶n(C)=2.0∶1.2∶1.0的粉末配比,在1 350℃热压烧结1.0h,可合成出高纯度单相Cr_2AlC陶瓷。当烧结温度较低时合成产物主要为Cr_2AlC、Cr_2Al和Cr_7C_3;当烧结温度超过1 450℃时Cr_2AlC陶瓷会分解为Cr_7C_3。Cr_2AlC陶瓷的干摩擦因数和磨损率均随摩擦载荷的增加呈现出先增加后降低的趋势,当载荷为50N时,干摩擦因数和磨损率达到最大值。     

放电等离子合成Ti3AlC2/TiB2复合材料的制备及性能研究

采用放电等离子烧结方法研究了Ti3AlC2/TiB2复合材料的制备和不同TiB2含量(体积百分数)对Ti3AlC2/TiB2性能的影响.研究表明,在1 250℃,30 MPa压力和保温8 min条件下烧结,可以得到相对密度达98%以上的致密Ti3AlC2/TiB2块体材料;在Ti3AlC2中添加TiB2能大幅度提高材料的硬度;Ti3AlC2/TiB2维氏硬度达到10.39 GPa,电导率达到3.7×106 S·m-1当TiB2含量为10%时,抗弯强度为696 MPa,断裂韧性为6.6 MPa·m1/2,但当TiB2含量继续增加时,由于TiB2的团聚和TiB2抑制Ti3AlC2晶体的生长导致了材料的抗弯强度和断裂韧性的下降.     

钙钛矿型La1-xBxMnO3(B=Sr,Ca)粉体及块体材料的制备研究

钙钛矿型La1-xBxMnO3 (B= Sr,Ca)陶瓷具有随温度变化改变自身红外发射率的性质,是当前国内外航天器智能热控材料的研究热点.本工作采用固相反应合成法制备La1-xBxMnO3 (B=Sr,Ca)粉体,研究了粉体的反应过程及工艺参数对粉体纯度的影响,实验结果表明,在1200℃下保温6h后,合成出的粉体具有较高纯度.在合成高纯度粉体的基础上,采用冷压成型-常压烧结工艺制备La1-xBxMnO3( B= Sr,Ca)块体材料,研究了烧结温度、保温时间等工艺参数对块体质量的影响,结果表明,在1200～1400℃范围内,随着烧结温度的提高,块体的密度和维氏硬度提高,当烧结温度为1400℃时,块体的密度最高,质量最好;而在烧结温度1400℃下,随着保温时间的延长,块体的密度进一步提高,而维氏硬度却有所下降.     

烧结温度对Cf/SiC复合材料结构及性能的影响

以碳纤维为增强体, 热压烧结制备了C_f/SiC复合材料, 研究了烧结温度对C_f/SiC复合材料密度、结构及性能的影响. 研究发现: 提高烧结温度能够促进C_f/SiC复合材料的致密度; 当烧结温度低于1850℃时, 升高烧结温度, 复合材料的强度和断裂韧性也随之提高. 当烧结温度为1850℃时, 复合材料的性能最优, 弯曲强度达500.1MPa, 断裂韧性为16.9MPa·m ^1/2. 当烧结温度达到1880℃时, 复合材料性能反而下降.     

掺Si对热压合成Ti2AlC/Ti3AlC2的影响及理论分析

采用热压工艺以Ti、Al、Si元素粉和活性炭为原料,分别以2.0Ti/1.1Al/1.0C(摩尔比)及以0.1和0.2mol的Si取代Al,合成了Ti2AlC/Ti3AlC2块体材料.通过建立Ti2AlC、Ti3AlC2和掺Si的计算模型,计算了平均原子净电荷和平均共价键键级.结果表明:以元素粉2.0Ti/1.1Al/1.0C为原料在1450℃热压60min合成只含有非常少量Ti3AlC2的Ti2AlC材料;当Si取代Al达到0.2mol时,作用非常明显,表现为使同一温度下Ti3AlC2含量增加而Ti2AlC含量减少.另外,应用掺Si后对原子净电荷和共价键键级的影响解释了实验结果.     

添加TiC和Ti3AlC2对燃烧合成Ti3AlC2粉体的影响

Ti、Al、C和TiC组成的Ti:Al:C=3:1.1:1.8（摩尔比）体系的燃烧合成实验结果表明，当在体系中未加入TiC时，得到的主要是TiC，但加入TiC后燃烧合成产物主要是Ti3AlC2，且Ti3AlC2量随TiC加入量的增加而增加，随燃烧反应体系温度的降低而增加；加入晶种Ti3AlC2有利于合成Ti3AlC2相物质。     

烧结温度对Cf/SiC复合材料结构及性能的影响

以碳纤维为增强体, 热压烧结制备了C_f/SiC复合材料, 研究了烧结温度对C_f/SiC复合材料密度、结构及性能的影响. 研究发现: 提高烧结温度能够促进C_f/SiC复合材料的致密度; 当烧结温度低于1850℃时, 升高烧结温度, 复合材料的强度和断裂韧性也随之提高. 当烧结温度为1850℃时, 复合材料的性能最优, 弯曲强度达500.1MPa, 断裂韧性为16.9MPa·m ^1/2. 当烧结温度达到1880℃时, 复合材料性能反而下降.     

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.……     

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...     

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.     

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.……     

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.     

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.     

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 ...