铸态及喷雾沉积态ZA27合金的阻尼性能比较

利用喷雾沉积快速凝固技术制备了ZA27合金,探讨了该工艺对ZA27合金组织和阻尼性能的影响,并与铸态的同类合金作了对比。结果表明,无论是喷雾沉积态还是铸态,随着频率的减小或温度的升高,ZA27合金的阻尼值增大,且在试验范围内阻尼性能不随应变振幅变化。室温下,喷雾沉积态ZA27合金的阻尼性能高出铸态合金的约1倍,如振动频率为1Hz,30℃时喷雾沉积ZA27合金的阻尼可达1.62×10-2。但当温度高于一定值以上时,铸态的阻尼性能高于喷雾沉积态的。阻尼的这种变化是与其组织密切相关的。     

铸态ZK51镁合金的显微组织及其阻尼行为

研究了铸态ZK51镁合金的显微组织及其阻尼行为.结果表明,铸态ZK51镁合金显微组织由α-Mg及少量分布在晶界或晶内的Mg7Zn3相组成.室温下,铸态ZK51镁合金的阻尼值随振动频率变化不明显,只随应变振幅的增大而明显增大.在高温200℃条件下,材料阻尼性能随振动频率的增加而呈现指数下降趋势.铸态ZK51镁合金在280℃附近出现热激活弛豫阻尼峰.合金的阻尼行为可采用Granato-Lücke位错阻尼理论解释.     

Ca对AZ91显微组织及力学性能的影响

用气体保护法制备了含的合金,研究了对合金显微组织和力学性能的影响。结果表明,Ca能显著细化AZ91合金铸态和时效态的组织,改善了铸态组织形态。Ca的加入未形成新相或沉淀物,而是溶入β-Mg17Al12相中,并提高了β-Mg17Al12相的热稳定性。Ca的加入可以明显提高AZ91合金室温及高温下的拉伸性能。     

含钪Al-Cu-Li-Zr合金的组织与性能

为了研究微量Sc对Al-3.5Cu-1.5Li-0.12Zr合金组织与性能的影响,采用铸锭冶金法,制备了4种不同Sc含量的Al-3.5Cu-1.5Li-0.12Zr合金.采用室温拉伸力学性能实验、金相显微镜和透射电镜研究了微量Sc对Al-3.5Cu-1.5Li-0.12Zr合金微观组织和拉伸性能的影响.结果表明:添加0.1%Sc能消除铸态合金的枝晶组织,有效地抑制了再结晶的发生,具有一定的强化作用和明显的增塑效应;添加O.15%Sc和0.25%Sc能显著细化合金铸态的晶粒组织,但添加0.15%Sc不能抑制合金固溶过程中再结晶;添加0.25%Sc会促进合金固溶过程中的再结晶,从而降低合金的强度.合金中较适宜的Sc加入量为0.10%～0.15%,此时合金既具有较高的强度,又兼具较好的塑性.     

铸态BeAl合金的低频阻尼特性研究

利用动态热机械分析仪研究了铸态BeAl合金的低频阻尼性能.研究结果表明,在小位移振幅下(A＜10μm)铸态BeAl合金的内耗值在30～200 ℃范围内基本不变,且与频率无关,温度高于200 ℃时,随温度的升高而急剧增大,并随频率增大而降低,分析认为,界面滑移、热错配应变和位错脱钉是铍铝合金阻尼值急剧变化的原因.得到了BeAl合金阻尼的线性拟合公式,利用该公式可以估算此合金的阻尼大小及行为,并揭示BeAl合金的阻尼机理.     

微量Sc和Mn对Al-Mg合金组织与性能的影响

通过显微组织观察和室温拉伸试验,研究了微量Sc和Mn对Al-5Mg合金显微组织和拉伸性能的影响.结果表明:在Al-5Mg合金中添加微量Sc、Mn消除了合金铸态枝晶组织,强烈抑制合金退火过程中的再结晶,明显提高了合金的强度,其退火态合金的抗拉强度和屈服强度分别提高了19～67MPa和25～64MPa;复合添加微量Mn和Sc比单独添加Mn或Sc的强化作用和抑制再结晶效果更显著;合金强化机制为亚结构强化和Mn、Sc与铝的金属间化合物弥散质点的析出强化.     

硅合金化ZA27合金的阻尼性行为

硅合金化ZA27合金具有良好的耐磨性能,但其阻尼性能(Q-1)研究尚不深入.本文利用多功能内耗仪研究了铸态ZA27合金和向ZA27合金中加入4%Si的合金(下称ZA27-4%Si合金)的阻尼行为和相对动态模量,分析了两种合金的阻尼机理.结果表明两种合金的阻尼性能随频率降低和温度升高而增大,阻尼值不随应变振幅变化.ZA27合金和ZA27-4%Si合金具有较高的阻尼性能,在0.1Hz下,合金的室温阻尼分别为6.87×10-3与5.83×10-3.合金的相对动态模量随应变频率提高而增大.100℃以下,ZA27-4%Si合金的相对动态模量不随温度变化.研究表明合金的阻尼是由合金晶界和相界面滑动、位错振荡以及各相的热膨胀系数和弹性模量间差造成的微塑性变形共同造成的.认为ZA27-4%Si合金具有良好耐磨性能和减振性能和强度,适合作为滑动轴承合金材料.     

喷射成形高锰ZA35合金的工艺及组织研究

利用优化工艺参数的喷射成形技术制备含Mn3.5%(质量分数,下同)的ZA35合金坯,比较了铸态和喷射成形态合金的微观组织.研究表明:喷射成形态合金晶粒细小,组织分布均匀;元素Mn在铸态组织中主要以大量富Mn独立硬化相分布于晶界或晶界附近,喷射成形合金组织中富Mn相消失,元素Mn溶入基体,固溶度明显提高.元素Mn在铸态和喷射成形态合金基体中分布规律一致,即在α富铝相中的固溶度显著高于在η富锌相中的固溶度.热挤压后,喷射成形3.5%Mn-ZA35中有类似纳米级晶须状和颗粒状的MnAl6析出.     

微量钪对高Cu/Mg比Al-Cu-Li-Mg合金组织与性能的影响

利用金相显微镜、透射电子显微镜和拉伸试验等手段,研究了微量Sc对高Cu/Mg比Al-3.5Cu-1.5Li-0.5Mg-0.12Zr合金组织和拉伸性能的影响.结果表明:在Al-3.5Cu-1.5Li-0.5Mg-0.12Zr合金中加入0.10%Sc消除了合金铸态枝晶组织,有效抑制合金再结晶,明显提高了合金的强度和塑性,但晶粒细化效果不明显;添加0.15%和0.25%Sc显著细化合金铸态晶粒组织,塑性随Sc增加而提高,但添加0.25%Sc促进合金再结晶,合金强度显著降低.     

添加Sc、Zr和退火对Al-Si合金铸态力学性能的影响

使用OM、TEM、SEM、显微硬度和室温拉伸等手段研究了Sc和Zr的复合添加对Al-5.5Si合金铸态的组织和性能的影响,以及在不同温度退火后其性能的变化规律。结果表明,Sc、Zr的添加使Al-5.5Si合金的硬度提高了33%、抗拉强度提高了38%、屈服强度提高了52%、延伸率基本上不变。在Al-5.5Si合金中复合添加Sc、Zr使α-Al的平均晶粒尺寸从203 μm减小到130 μm,在α-Al基体中析出大量的Al₃(Sc_1-xZr_x)纳米粒子(10~15 nm),并使共晶Si内的层错或微孪晶的密度显著提高。退火温度对铸态合金的性能有较大的影响：在较低温度(低于160℃)退火时合金的硬度呈上升趋势,而在较高温度(高于280℃)退火时合金的硬度呈显著下降趋势。这些结果与二次析出的纳米Si相密切相关。     

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.     

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.     

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.     

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.