激光选区熔化纳米SiC/AlSi7Mg复合材料微观组织及力学性能EI北大核心CSCD

采用机械混合法制备纳米SiC/AlSi7Mg混合粉末,利用激光选区熔化技术(selective laser melting,SLM)成形纳米SiC颗粒增强AlSi7Mg复合材料,观察和分析试样的相对密度、物相和微观组织,并测试材料的硬度和拉伸性能。结果表明:SLM成形纳米SiC/AlSi7Mg复合材料试样的相对密度随着扫描速度和扫描间距的增大均呈现先增加后减少的趋势,相对密度最高可达99.75%;试样微观组织与SLM成形铝合金相似,Si相呈网状结构均匀嵌入α-Al基体中,且在Al基体中存在与Si分布相似的纳米SiC团聚物及Mg_(2)Si相;与AlSi7Mg相比,复合材料微观组织由柱状晶转化为等轴晶,且晶粒明显细化(平均晶粒尺寸为1.36μm);由于SiC的加入,产生细晶强化和固溶强化,试样的硬度和强度均明显提高,硬度最高达到137.3HV,抗拉强度达到448.3 MPa,屈服强度达到334.7 MPa,但伸长率下降至3.9%,断裂模式主要为脆性断裂。     

纳米WC增强选区激光熔化AlSi10Mg显微组织与力学性能EI北大核心CSCD

为了进一步增强选区激光熔化(SLM)成型AlSi10Mg合金的性能,采用物理混合方法混合纳米WC与AlSi10Mg得到WC质量分数为0.1%的WC/AlSi10Mg复合材料,利用选区激光熔化成型机制备试样块。通过对比同种工艺制备的AlSi10Mg试样,探究纳米WC对其微观组织形成、演变规律及其组织对力学性能的影响。结果显示,WC/AlSi10Mg粉末球形度好,粒度分布集中在20~60μm。WC/AlSi10Mg试样致密度达到99%以上,硬度约为158.89HV,相比AlSi10Mg试样增加了14.58%。WC/AlSi10Mg试样组织生长均匀、致密,有明显的熔池线。晶粒内部为α-Al基体,边界为夹杂着WC的共晶Si相。WC/AlSi10Mg试样屈服强度达到337.75 MPa,抗拉强度高达514.00 MPa,伸长率为3.78%,相比同种工艺AlSi10Mg试样分别增加了4.73%,6.25%和35.97%。因此,SLM成型WC/AlSi10Mg纳米复合材料零件相比AlSi10Mg零件具有更好的应用前景。     

TiB2/AlSi10Mg激光选区熔化成形工艺研究

目的 针对TiB2/AlSi10Mg开展激光选区熔化成形研究,获得工艺参数影响规律并优化工艺参数.方法 采用正交试验法设计三因素四水平正交试验,进行TiB2/AlSi10Mg激光选区熔化成形,分别研究激光功率、扫描速度、扫描间距等3种工艺参数对TiB2/AlSi10Mg致密度和硬度的影响规律,分析激光能量密度对铝合金内...     

激光增材制造24CrNiMo合金钢显微组织特征EI北大核心CSCD

采用激光选区熔化技术和激光熔化沉积技术制备24CrNiMo合金钢单道和块体样品,研究两种激光辐照条件下24CrNiMo低合金钢的相组成、微观组织、织构特征和显微硬度。结果表明:两种方法制备的24CrNiMo合金试样的相组成均为α-Fe相以及少量的Fe 3C;SLM成形单道沉积样品的晶粒取向随机、无序,无明显的择优取向,而LMD成形单道沉积样品的择优取向为(110)〈101〉面织构;SLM成形块体样品的晶粒在平行于沉积方向上存在较弱的〈111〉织构,LMD成形块体样品的晶粒存在外延生长取向为〈111〉的强织构;SLM成形试样的显微组织主要为下贝氏体,而LMD成形试样的显微组织以板条贝氏体为主;具有细小晶粒和下贝氏体组织的SLM成形试样的平均显微硬度高于LMD试样。     

电子束选区熔化成形Ti_(2)AlNb合金微观组织与性能EI北大核心CSCD

Ti_(2)AlNb基合金由于具有优异的高温比强度、高温抗蠕变性能和较高的断裂韧度,因而被认为是替代传统镍基高温合金最具潜力的材料。采用电子束选区熔化(selective electron beam melting,SEBM)技术成形Ti-22Al-25Nb合金,通过工艺优化获得高致密度(5.42-5.43 g/cm^(3))的成形试样。研究了沉积态和热等静压(hot isostatic pressing,HIP)态试样的显微组织演变、物相演变及其对力学性能的影响。结果表明:沉积态和HIP态组织呈现出沿成形方向的柱状晶结构,且均由B2,O和α_(2)相组成,沉积态试样中的O/α_(2)相自上而下逐渐增加,HIP后组织趋于均匀化,且相对沉积态,析出相的宽度缩小、数量减少。沉积态试样中析出相较多的下部区域具有更高的显微硬度((345.87±5.09)HV),HIP后试样硬度值增加至388.91-390.48HV。沉积态试样室温抗拉强度和伸长率分别为(1061±23.71)MPa和(3.67±1.15)%,HIP后抗拉强度增加至(1101±23.07)MPa,伸长率降低至3.5%。     

退火态激光选区熔化成形AlSi10Mg合金组织与力学性能

AlSi10Mg合金具有高比强度、高耐磨性等优良特点。由于其成分接近共晶点,成形性能良好,被广泛应用于激光选区熔化技术。然而其热处理制度仍然沿用传统铸态合金的热处理规范,影响了其性能的充分发挥。本工作采用激光选区熔化技术制备了AlSi10Mg合金,并研究了沉积态和后续热处理过程中组织演化规律及其对室温力学性能的影响机制。研究发现：沉积态组织由沿沉积方向生长的α-Al柱状枝晶及枝晶间网状Al-Si共晶组成,具有强烈的〈100〉方向织构,沉积层由三部分组成,分别是细晶区、粗晶区及热影响区,抗拉强度389.5 MPa,伸长率4%。退火过程中,共晶Si破碎、球化,基体中过饱和Si不断析出长大。当退火温度从200 ℃提高到500 ℃时,Si颗粒发生Ostwald熟化,平均尺寸增长了23倍。经过300 ℃和500 ℃退火处理后,试样抗拉强度分别为287.0 MPa和268.0 MPa,但伸长率分别提高到10.3%和17.2%。     

选区激光熔化AlSi10Mg合金不同温度原位拉伸变形行为及断裂机理研究

为了提高选区激光熔化AlSi10Mg合金在航空航天领域的应用,基于自主研发的原位SEM高温拉伸台,本文对比分析了原位拉伸非校准样品的选区激光熔化AlSi10Mg合金在室温、200、300 ℃条件下的力学性能与显微组织动态演化,并总结了断裂机理。结果表明,选区激光熔化AlSi10Mg合金的显微结构由α-Al基体、共晶Si和大量的气孔组成,且共晶Si呈连续网格状均匀分布在α-Al基体上。随着温度的升高,选区激光熔化AlSi10Mg合金的强度降低。屈服强度从室温的207 MPa降低到300 ℃时的52 MPa,极限抗拉强度从室温的304 MPa降低到300 ℃时的71 MPa,延伸率则随温度的升高而增大,从室温的7.4%增大到300 ℃时的59.5%。室温拉伸过程中试样并未出现明显的颈缩现象,而是随着温度的升高,试样的颈缩现象逐渐明显,表明试样经历了更加充分的塑性变形, 并且随着温度的升高,试样的断裂位置越来越偏离标距段中心。通过对试样变形行为的研究发现,200 ℃时,变形主要集中在晶内,发生晶内滑移;而300 ℃时滑移主要集中在晶界,导致晶界滑移。由于试样表面及内部存在大量缺陷,因此,室温下选区激光熔化AlSi10Mg合金的断裂机理为熔池边界的组织突变结合孔洞连通造成的准解理断裂。随着温度的升高,由于初始孔洞边缘的应力集中产生新的孔洞形核,新形核的孔洞与相邻孔洞相连通,导致试样的最终断裂。     

激光增材制造高温合金原位增强钛合金复合材料的组织与力学性能

采用激光选区熔化成形（selective laser melting,SLM）技术制备TCGH(TC4+GH4169)复合材料,探究TCGH钛合金复合材料的最佳成形工艺参数,并研究沉积态试样和热处理试样的显微组织与力学性能。结果表明：TCGH钛合金复合材料的最佳工艺参数为扫描速率900 mm/s、激光功率150 W,致密度达到99.5%以上。GH4169粉末的添加改变了TC4钛合金材料的固态相变行为,沉积态组织呈现明显高温凝固特征,使得逐行扫描搭接和逐层扫描堆积成形特征变得明显,沿打印方向原始粗大柱状β晶粒尺寸明显减小,复合材料抗拉强度提升。与沉积态试样相比,950℃热处理后,试样显微组织转变为近等轴组织,同时随着热处理温度上升,第二相的回溶导致复合材料的固溶强化作用占主导地位,使得复合材料抗拉强度和塑性均得到提升。     

激光快速成形GH4169合金显微组织与力学性能

利用GH4169合金粉末进行激光快速成形实验,制备出GH4169合金块状试样,并进行固溶时效热处理。利用扫描电镜(SEM)及能谱分析(EDS)等方法分别对激光成形沉积态及固溶时效态试样进行显微组织及元素偏析分析,并测试显微硬度、室温及高温拉伸性能。结果表明:沉积态微观组织为生长方向不一的细长柱状树枝晶,组织细小致密;经过固溶时效热处理后晶粒得到细化,晶粒内部仍保留枝晶亚结构;固溶时效态试样较沉积态显微硬度及抗拉强度大幅提高,塑性有所下降,但整体优于锻件技术标准。断口形貌表现为韧性穿晶断裂方式。     

铸态Mg-4Al-2Si合金的显微组织与力学性能

采用重力铸造法制备Mg-4Al-2Si(AS42)镁合金,研究了铸态合金的显微组织和室温力学性能。结果表明:铸态AS42合金主要由α-Mg基体、β-Mg17Al12相及Mg2Si相组成;β-Mg17Al12相呈网状和棒状分布于晶界上,粗大的汉字状Mg2Si相沿晶界或穿晶分布,多边形块状Mg2Si相随机分布于基体组织中。铸态合金的硬度为64.5 HV,室温抗拉强度为113.5 MPa,屈服强度为86 MPa,伸长率为4.1%;拉伸断裂形式为准解理脆性断裂。     

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.     

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