溶质对单相纳米晶材料晶粒长大行为的影响

从热力学角度来看,溶质在晶界偏聚,通过降低晶界能来降低晶粒长大的驱动力,从而抑制晶粒长大。从动力学角度来看,溶质与晶界交互作用,钉扎晶界,使晶界迁移速率降低,从而抑制晶粒长大。本文从热力学和动力学两方面综述了溶质对单相纳米晶材料晶粒长大行为的影响,并展望了其发展方向。     

Cu纳米晶块体的制备及纳米晶粒长大动力学研究

采用高能球磨的方法制取金属纳米晶粉末，然后利用放电等离子烧结（SPS）技术制备出金属纳米晶块体材料。设计系列实验研究金属纳米晶材料的晶粒长大行为，获得了纳米晶粒长大的动力学规律。根据已有的工作基础和对实验结果的深入分析，确定动力学参数对稳定相晶粒长大行为的影响。实验发现了高能球磨配合SPS技术制备的Cu纳米晶块体发生快速晶粒长大的临界温度，并结合纳米晶界过剩体积与过剩自由能的关系，分析了纳米晶粒组织的能量因素对晶粒长大行为及动力学的影响。     

影响Cu-Sn合金电阻率的因素

利用量子力学理论分析了成分变化对Cu-Sn合金电阻率影响的微观机理;探讨了铸态、正火态、轧制态和回火态存在的一些影响因素,如固溶体中的溶质含量、晶界、晶体缺陷和应力等对Cu-Sn合金电阻率影响的宏观机理。实验结果表明:正火处理会增加Sn原子在Cu晶粒内部的固溶量,使合金的电阻率上升;大变形量轧制后,Cu晶粒被挤压变长,晶界厚度减小,铸造缺陷基本消失,自由电子被散射的几率减小,Cu-Sn合金的电阻率会大幅度下降;回火处理可消除微观组织中的部分应力,使晶格畸变减轻和位错密度降低,可获得更低的电阻率。     

直接晶化法制备块状纳米材料的探索──Ⅰ脉冲电流作用下无序金属介质的成核理论

利用经典热力学和连续介质电动力学理论计算了脉冲电流作用下无序介质（包括金属熔体和非晶态金属）的成核率．结果表明：对于无序介质的晶化过程，随脉冲电流密度增加，形核率成指数增大；超短时脉冲有可能使熔体直接冷凝成大块纳米晶材料，并能限制已经形成的纳米晶粒的长大．     

溶质原子在再结晶运动晶界上偏聚的研究

Ｂ＾１０（ｎ，α）Ｌｉ＾７裂变反应的径迹显微照相技术被用来研究含硼Ｆｅ－３０％Ｎｉ合金高温热变形再结晶过程中硼在晶界上的偏聚行为，实验表明，含硼Ｆｅ－３０％Ｎｉ合金１０００℃热变形２０％再结晶过程中，运动晶前方发生硼偏聚而后方发生贫硼现象，而在静止晶界上看不到硼偏聚，随着再结晶新晶粒的长大，运动晶界上的硼偏聚变弱。本文提出，可以用晶界对溶质原子热运动散射的量子理论来解释溶质原子在运动晶的偏聚现象。     

纳米材料晶粒生长理论的研究进展

实验研究表明,纳米材料的晶粒生长速率远低于传统晶粒长大理论所预测的生长速率,为解释这一异常的晶粒生长行为,研究者提出了各种理论模型。综述了纳米晶粒生长理论模型的研究现状:第一类为动力学模型,通过钉轧晶界实现延缓晶粒的生长,起钉轧晶界作用的有溶质原子、三叉晶界和第二相等;第二类是热力学模型,通过降低晶界能来降低晶粒生长的驱动力,从而实现延缓晶粒的生长,如溶质原子偏析晶界和空位注入模型等。对各种理论模型进行了描述和分析,并展望了其发展方向。     

脉冲电沉积纳米晶Ni-Co合金镀层热稳定性的研究

采用X射线衍射(XRD)、能谱分析(EDS)等方法研究脉冲电沉积法制备的纳米晶Ni-Co合金镀层的组织结构和合金成分.测定不同退火温度下纳米晶Ni-Co合金镀层的显微硬度,并着重研究Ni-23.5%Co(质量分数)合金的热稳定性,结果表明:随着退火温度的升高,纳米晶Ni-Co合金在低温退火后显微硬度有所升高,在250℃时达到最高值,然后随退火温度的继续升高而降低.纳米晶Ni-23.5%Co合金镀层的晶粒尺寸逐渐增大,从原始晶粒尺寸13.5nm长大到300℃时的98.5nm,在升温速率为20K·min-1的DSC曲线中,Ni-23.5%Co合金在约300～350℃一直是低能放热,随后出现明显的放热峰,其峰值温度为372℃,放热焓为14.22J·g-1.通过测定不同升温速率条件下的DSC曲线峰值温度,由Kissinger方程求得纳米晶Ni-23.5%Co合金镀层的晶粒长大激活能为212.SkJ/mol.     

EXPLORATION ON THE FABRICATION OF BULK NANOCRYSTALLINE MATERIALS BY DIRECT-NANOCRYSTALLIZING METHOD Ⅰ. Nucleation in Disordered Metallic Media by Electropulsing

利用经典热力学和连续介质电动力学理论计算了脉冲电流信息处理作用下无序介质（包括金属熔体和非晶态金属）的成核率。结果表明：对于无序介质的晶化过程，随脉冲电流密度增加。形核率成指数增大；超短时脉冲有可能使熔体直接冷凝成大块纳米晶材料，并能限制已经形成的纲米晶粒的长大。     

中科院揭示孪晶辅助纳米晶粒生长机制

正近日,中科院金属研究所沈阳材料科学国家(联合)实验室研究员张广平带领团队,通过对纳米尺度金属薄膜疲劳加载下晶粒长大行为的原子尺度研究,揭示了"孪生辅助纳米晶粒长大"的全新物理机制,相关论文在线发表于《自然-通讯》上。尽管金属中的晶界具有阻碍位错运动、强化材料的重要作用,但当材料的晶粒尺寸减小到纳米尺度时,晶界变得不     

CdO纳米晶的固相合成及晶化动力学研究

以CdCl2和Na2CO3为原料,NaCl为稀释剂,利用固相反应合成前驱体,再经焙烧合成CdO纳米晶.用x-射线衍射(XRD)分析了不同焙烧温度对合成CdO晶粒尺寸的影响.研究结果表明:按Scherrer公式计算合成CdO纳米晶的晶粒尺寸在30～44nm,焙烧温度越高,晶粒尺寸越大;根据前驱体不同升温速率下的差热(DTA)曲线,用Kissinger 和Ozawa法计算合成CdO纳米晶的活化能分别为164.7kJ/mol和175.6kJ/mol,差别不大;根据晶粒生长动力学理论计算CdO晶粒长大的活化能为12.2kJ/mol,表明热处理过程CdO纳米晶粒的长大主要以界面扩散为主.     

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.……     

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 ...