镍基单晶高温合金凝固缺陷研究进展

镍基单晶高温合金的凝固缺陷对其力学性能有很大的影响,减少和控制凝固缺陷对提高合金性能和降低成本具有重要意义。综述了镍基单晶高温合金定向凝固过程中可能出现的几个重要缺陷,包括缩松、雀斑、晶体取向的偏离和杂晶,重点讨论了这些缺陷的特点和产生的机理,并从合金成分、工艺参数、铸件结构等方面分析了凝固缺陷的影响因素,指出了减少单晶高温合金凝固缺陷的措施。     

镍基单晶高温合金杂晶缺陷的研究进展

随着单晶涡轮叶片结构的不断优化和高温合金中难熔元素添加量的增大,镍基高温合金单晶叶片在凝固过程中更易出现杂晶、条纹晶、枝晶碎臂、小角度晶界等缺陷。其中,杂晶是单晶叶片制备过程中最常见的一类凝固缺陷,严重影响单晶叶片的成品率。为了减少该类凝固缺陷的产生,提高叶片的成品率,研究镍基单晶高温合金杂晶缺陷的形成机制、影响因素及其控制措施,对提高单晶叶片的服役性能具有重要意义。因此,关于定向凝固过程中杂晶缺陷的形成机制、影响因素及其控制措施的研究,引起了国内外研究者的广泛关注。本文综述了单晶叶片的制备技术,分析了籽晶法和选晶法制备单晶叶片过程中不同位置杂晶的形成机理,分别讨论了选晶段杂晶、籽晶回熔区杂晶、缘板杂晶的影响因素和控制措施,并对未来的研究方向进行了展望。     

静磁场对定向凝固镍基高温合金组织影响的研究进展

综述了国内外静磁场对镍基高温合金组织影响的研究现状,重点分析了施加不同方式、强度的静磁场对定向凝固镍基高温合金枝晶组织、元素偏析、凝固缺陷及高温力学性能的影响规律,并从变截面处杂晶的控制、晶体取向偏离的控制以及对凝固特性的影响机制等方面提出了静磁场在定向凝固镍基高温合金研究中潜在的发展方向。     

不同元素对镍基合金铸态组织的影响

镍基单晶高温合金是一种应用于航空发动机涡轮叶片的重要合金,镍基单晶高温合金能够在航空发动机涡轮叶片工作时的恶劣工况条件下获得良好的使用性能。镍基单晶高温合金的性能与镍基单晶高温合金的凝固组织有着密切的联系,为获取更好的使用性能需要了解不同元素对镍基单晶高温合金铸态组织的影响,并以此为基础开发出性能更好的镍基单晶高温合金用,以提高航空发动机的性能。     

难熔元素对镍基单晶高温合金凝固特性及组织的影响

镍基单晶高温合金的性能与难熔元素Re、W、Ta等的含量之间有着紧密的联系.总结了在镍基单晶高温合金的发展过程中难熔元素添加的特点,综述了难熔元素对镍基单晶高温合金的凝固特性与凝固组织的影响,并指出了其中存在的问题,展望了未来研究发展的方向.     

单晶 Ni 基高温合金侧向约束条件下的凝固行为

研究了侧向约束条件下单晶 Ni 基高温合金的凝固行为及溶质再分配。实验结果表明:侧向约束条件对单晶 Ni 基高温合金的凝固组织、溶质偏析及溶质再分配均具有极为强烈的影响。侧向约束条件即试样断面变化对单晶 Ni 基高温合金凝固过程的影响,实质上是局部凝固工艺参数的影响。本文研究结果对实际单晶 Ni 基高温合金铸件凝固组织的控制和生产具有重要的指导意义。     

CMSX-3单晶合金的微观组织研究

镍基单晶高温合金是重要的航空燃气轮机涡轮叶片材料。本文利用光学金相、SEMTEM等分析手段研究了采用定向凝固造晶法制造的CMSX－3单晶合金的微观组织。对其铸态组织与γ＇形态做了描述与分析。     

单晶高温合金DD3亚结构超细化定向凝固工艺研究EI

利用ＺＭ定向凝固装置研究了镍基单晶高温合金ＤＤ３在高温度梯度（７００～１２００Ｋ／ｃｍ）定向凝固条件下的微观组织演化特征及其对工艺参数的响应函数，结果表明：该合金在高界面温度梯度条件下，柱晶生长速度范围向高速区扩展，从而使单晶亚结构细化成为可能。所得单晶棒中亚结构一次间距可比传统ＨＲＳ法定向凝固籽晶中相应尺度减小５～１０倍。本文还对其组织演化机制进行了分析。     

定向凝固过程中温度参数对含Re镍基单晶高温合金铸态组织的影响

研究了一种含Re为4.0%～5.5%(质量分数)的实验型镍基单晶高温合金在不同定向凝固结晶条件下铸态的宏微观组织特征,分析了凝固结晶温度参数对单晶完整性、显微疏松与共晶含量、枝晶偏析等的影响。结果表明:高的熔体过热处理温度不仅促进合金元素分布的均匀化,同时降低了高Re和高难熔元素含量的单晶合金结晶缺陷的倾向性,提高了单晶完整性。合金熔体过热温度、铸型温度/浇注温度的适度提高有利于枝晶间的补缩,并减少显微疏松。     

Ru对镍基单晶高温合金凝固特性、TCP相析出及蠕变性能影响的研究进展EI北大核心CSCD

镍基单晶高温合金因优异的高温力学性能而被广泛应用于航空发动机和地面燃气轮机的涡轮叶片等关键热端部件。Ru元素作为第四代、第五代镍基单晶高温合金的主要特征元素,其添加对合金从凝固特性到最终的服役性能都起到关键的影响。本文从镍基单晶高温合金的凝固特性、凝固组织、TCP相析出及蠕变性能等方面出发,综述了Ru元素对镍基单晶高温合金影响的研究进展,系统分析了Ru的添加对合金凝固路径、凝固特征温度、微观偏析等凝固特性及共晶、碳化物等凝固组织的影响规律,并重点探究了Ru的添加能抑制TCP相析出及提高合金蠕变性能的原因。目前由于多组元交互作用对组织与性能影响机理的复杂性,使得含Ru高温合金的成分设计与优化具有更高的挑战,建议未来含Ru高温合金的相关研究从富Ru新相的析出原因及抑制、Ru添加对凝固缺陷的影响及Ru与其他元素交互作用对“逆分配”效应及TCP相析出的影响机制等方面做进一步探究,为发展新型高性能含Ru高温合金的设计提供思路。     

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.     

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.