晶粒尺寸对Cu-30%Zn合金形变孪晶厚度的影响

对于面心立方结构的纳米金属,晶粒尺寸对孪生厚度(孪生核)的影响虽已有研究,但仍有待深入。本论文以Cu-30%Zn合金为模型材料,通过高压扭转变形技术、等径角挤压连同轧制技术变形得到晶粒尺寸在5~500nm的样品。透射电子显微镜观察发现:变形孪晶的片层厚度随晶粒尺寸的减小而减小,当晶粒尺寸小于20nm以后,孪晶厚度为(111)晶面间距(层错);另外,层错存在于各个不同尺寸范围的晶粒内,表明层错不受晶粒尺寸影响。研究结果表明在低层错能超细晶材料中,孪生变形是通过从晶界连续发射不全位错(层错)形成的。     

AZ31镁合金微结构关联的孪生形核与长大统计分析

为了揭示金属镁合金晶粒大小、晶向及晶界倾角等微结构与孪生形核及长大之间的关联性,通过EBSD技术获取大量诸如晶粒尺寸、晶向及晶界倾角等微结构以及晶内孪生形核数、孪晶厚度等数据进行统计分析。对应变为4.9%的镁合金微结构的统计分析表明:晶粒大小、晶界倾角等微结构分布基本符合概率函数Weibull分布特征;大晶粒、高Schmid因子、小角度晶界有利于孪生形核,而孪晶长大对微结构的敏感度较弱;不是所有高Schmid因子的孪生变体都能够形核长大。由对孪生形核与长大随应变递增的演化分析结果可推测:相同晶粒内,不同位置对孪晶变体的形核强度有显著影响,很显然存在其他晶内微结构如缺陷、位错密度等对孪生形核产生重要影响;然而孪晶长大更多地受到晶内存在的孪生形核数和孪晶变体类型数量的强烈影响。本工作可为发展孪生形核长大与微结构的数学关系提供试验依据。     

选区激光熔化316L不锈钢高应变率压缩下的塑性变形行为

对选区激光熔化316L不锈钢(SLM-316L)的高应变率(1000、2000、3000 s^-1)压缩力学性能进行测试，用扫描电镜和背散射衍射(EBSD)等手段表征冲击加载前后试样的微观结构，并分析晶体结构的差异以及位错滑移、孪生行为等微观变形机制。结果表明：SLM-316L不锈钢在高应变率载荷作用下有显著的应变率强化效应，其微观组织由截面呈不规则多边形的柱状胞晶密排结构组成，高应变率加载使晶体取向的择优性降低、小角度晶界和孪晶界数量增加，且孪晶界在小角度晶界的交叉缠绕区分布密集，试样的塑性变形过程伴随着位错滑移及孪生行为。     

利用孪晶界面强韧化镁合金

轻质镁合金在航空航天、交通运输等领域的轻量化方面具有广阔的应用前景。孪生变形是六方结构镁合金室温下重要的变形机制,最近大量研究报道了利用预变形孪晶界面调控镁合金组织、织构和力学性能。系统综述了利用拉伸孪晶组织强化镁合金的研究进展。首先介绍了镁合金的主要变形机制及拉伸孪生的特点,然后系统总结了利用拉伸孪晶强化镁合金的研究进展,重点阐述了孪晶强化特点及主要准则,包括利用单一孪晶结构强化镁合金的特点及不足、利用复合孪晶结构实现三维强化的思路、复合孪晶实现三维强化的机制及复合孪晶结构的设计准则。最后展望了利用孪晶组织强化镁合金的发展方向。     

柱状多晶Mg-Gd-Y合金形变组织演变及形变硬化机制

利用定向凝固技术制备了生长取向集中于■、基面〈a〉滑移取向因子(Schmidfactor, SF)大于0.4的柱状多晶Mg-6.38Gd-0.45Y合金,并研究了实验合金室温拉伸形变行为。结果表明,形变初期,软取向柱状晶内首先启动■拉伸孪生协调应变。形变过程中■,拉伸孪晶界快速、大范围扩展,吞噬基体并使基体取向逐渐转为■,于是启动■压缩孪生和■双孪生协调应变。压缩孪晶和双孪晶易形成压缩孪晶带群,并贯穿整个晶粒,滑移或扩展的位错及拉伸孪晶界与压缩孪晶带群交织在一起,产生形变硬化,提高合金强度的同时也形成应力高度集中分布区域,成为微裂纹形成之地。     

镁合金塑性变形中孪生的研究

介绍了镁合金变形过程中孪生的晶体学、位错机理以及几何位向学;探讨了孪晶的形核、长大与演变机制;分析了孪生过程对塑性变形的作用;论述了影响孪生的几种基本因素,包括晶粒取向、变形温度、变形速度、晶粒尺寸、预变形.研究结果表明,镁合金塑性变形过程中孪生变形的作用在于,通过孪生过程改变晶粒取向或通过孪晶间或孪晶与滑移之间的相互作用,诱发新的滑移和孪生;孪晶也可抑制裂纹的产生和扩展,从而提高变形镁合金的室温塑性.     

Al_(0.3)CoCrFeNi高熵合金高压扭转过程中的组织结构演变

对面心立方(FCC)结构的Al_(0.3)CoCrFeNi高熵合金进行不同应变量的高压扭转实验,利用维氏硬度仪、电子背散射衍射、X射线衍射仪以及透射电镜系统分析变形引起的组织结构演变。结果表明:高压扭转过程中合金晶体结构并未发生改变,仍然保持为FCC结构,但引发其晶粒纳米化,平均晶粒尺寸达到30nm。晶粒细化主要是通过孪晶(包含初次孪晶与二次孪晶)、去孪晶(包含初次去孪晶与二次去孪晶)以及孪晶界分割晶粒的过程实现。孪晶和随后去孪晶的竞争作用导致孪晶宽度先减小后增大,初次孪晶和二次孪晶的最小宽度分别为2.7nm和0.9nm。     

高应变速率下等径角挤压高纯粗晶铝中的形变孪晶与退火孪晶

在室温下对铸态高纯粗晶铝进行一道次高应变率动态等径角挤压(D-ECAP)变形,利用电子背散射衍射技术(EBSD)研究挤压过程中所形成的孪晶。结果表明:利用D-ECAP能够在粗晶铝中同时制备出形变孪晶和退火孪晶,但两者在形态、Kernel平均取向差(KAM)以及与相邻晶粒的取向差三个方面存在较大差异。D-ECAP高应变率和大剪切变形使高层错能铝中形成了百微米级的形变孪晶,形变孪晶的形态为透镜状,后续变形使得孪晶界偏离∑3 60°〈111〉取向关系且KAM值主要集中于0.6°~1.8°。高应变率剪切变形下形成的大量层错和复杂的位错组态以及高形变储存能在变形温升的作用下促进了退火孪晶的形成。退火孪晶的形态较不规则,但孪晶界的取向关系更接近于∑3 60°〈111〉且KAM值主要集中于0.2°~0.5°。     

高锰Hadfield钢单向拉伸变形及断裂行为研究

本研究测试了高锰Hadfield钢室温下在大应变速率(分别为6×10~(-3)s~(-1)、6×10~(-4)s~(-1)、3×10~(-5)s~(-1)和6×10~(-6)s~(-1))范围内的单向拉伸变形的力学响应行为,分析了合金的变形行为及裂纹萌生与扩展规律。结果表明:在不同应变速率下均存在动态应变时效现象,且延伸率具有正的应变速率敏感性。拉伸变形后,奥氏体晶粒内产生了大量位错和层错,以及细小且相互平行的形变孪晶。应变硬化率随真应变的增加依次表现为"减小—增大—减小"三个演变阶段。其中,第二阶段的增大现象是形变孪晶的急剧增加而形成孪生硬化所致。垂直于拉伸变形方向分布的高密度滑移带是裂纹萌生的主要区域。裂纹扩展以沿垂直拉伸方向的穿晶形式为主,结合沿孪晶方向进行。高锰Hadfield钢的主要变形机制是滑移与孪生的相互竞争。     

TiAl有序金属间化合物中的层错带与变形孪晶

采用 TEM 衍衬试验研究了 TiAl+Mn 合金中层错带和变形孪晶的特征。结果表明:所观察到的层错带是一组在平行(111)面上的重叠层错,提出这种重叠层错是由柏氏失量■=1/6[112]的不全位错扫过相继平行(111)面时形成的。分析结果还表明,按上述机制所形成的重叠层错的取向与观察到的变形孪晶一致。因此,重叠层错实际上是变形孪晶的胚胎。基于以上对层错带及变形孪晶形成过程的认识,本文进一步探讨了第三元素对 TiAl 基合金孪生变形及延性的影响。     

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.     

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.     

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 ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.