放电等离子烧结NdFeB磁体的烧结特征研究

应用放电等离子烧结技术(SPS)制备新型SPS NdFeB磁体.利用扫描电子显微镜(SEM)观察磁体的显微组织,利用B-H回线仪测量磁体磁性能,利用阿基米德法测量样品密度.系统研究了稀土含量不同的两种NdFeB磁体的烧结特征.结果表明,SPS NdFeB磁体的烧结特征与传统烧结方式的特征不同,且与样品稀土含量密切相关;...     

微观组织调整和稀土含量对烧结NdFeB永磁腐蚀的影响

采用放电等离子烧结技术(SPS)制备了不同稀土含量的新型烧结NdFeB磁体,为了对比,采用传统烧结工艺制备了相同成分的磁体。测量了磁体在高压湿热环境的腐蚀行为。结果表明SPS磁体的耐腐蚀性明显优于传统烧结磁体,而且随着稀土含量的降低,烧结NdFeB磁体的耐腐蚀性能显著提高。     

放电等离子烧结NdFeB永磁材料的强韧化

分别采用放电等离子烧结技术(Spark Plasma Sintering,简称SPS技术)和传统烧结技术制备了成分为Nd12.2Pr2Dy2FebalAl1Nb0.3Cu0.2B6的烧结NdFeB永磁体.研究了所制备磁体的冲击韧性和抗弯强度,并利用扫描电镜(SEM)观察了磁体的显微组织形貌.结果表明:SPS技术制备的Nd-FeB永磁体的冲击韧性和抗弯强度较传统烧结磁体有显著提高,前者的冲击韧性与抗弯强度分别为Kc=0.955J/m2、σbb=402.25 Mpa,后者仅为Kc=0.709J/m2、σbb=278.97MPa.显微组织观察发现,SPS NdFeB永磁体的主相晶粒细小均匀、富钕相细小弥散且彼此隔断;断12表现为较明显的解理断裂特征;而传统烧结磁体主相晶粒较粗大、富稀土相粗大且彼此连接,断口呈明显的沿晶断裂特征.     

热处理工艺对块体纳米晶Fe3B/Nd2Fe14B复合磁体性能的影响

采用放电等离子烧结技术(Spark Plasma Sintering,简称SPS技术)将快淬Nd4.5Fe77B18.5薄带制备成块状纳米晶复合磁体.着重研究了热处理工艺对磁体密度、微观结构和磁性能的影响.结果表明,通过直接烧结得到的磁体具有超细纳米晶结构,合适的热处理可以消除残余非晶,得到较好的晶体结构和磁性能.但过高的热处理温度和较长的保温时间的增大会造成晶粒长大,结果导致磁性能的恶化.在最佳热处理条件下得到的磁体的磁性能为Br=1.014T,JHc=237.21 kA/m,(BH)max=61.85 kJ/m3.     

放电等离子烧结NdFeB磁体的氧化和腐蚀行为

采用放电等离子烧结技术制备了新型NdFeB磁体,研究了NdFeB磁体在湿热环境下的氧化行为和在电解质溶液中的电化学特性.在扫描电子显微镜下分析了磁体的显微组织结构和成分.结果表明,与传统烧结NdFeB磁体相比,新型磁体的显微组织特征为:主相Nd2Fe14B晶粒细小、均匀,富钕相在主相晶粒边界上分布较少,主要集中在三角晶界处.这种组织结构有效抑制了磁体沿富钕相发生的晶间腐蚀的过程,使磁体具有良好的耐腐蚀性能.     

放电等离子烧结新型NdFeB永磁材料工艺研究

采用放电等离子烧结技术制备了新型NdFeB磁体，研究了烧结工艺和热处理工艺对磁体的磁特性、尺寸精度及致密度的影响。同时利用B-H回线仪、扫描电子显微镜对其磁特性、显微组织结构进行了分析测试。结果表明，这种新型的烧结NdFeB磁体具有独特的显微组织结构，主相NdFe14B晶粒细小、尺寸均匀，富钕相弥散分布在主相边界上。获得最佳工艺条件下制备的磁体的磁特性为：最大磁能积(BHmax)240kJ／m^3，内禀矫顽力(Hci)1160kA／m，磁体的密度达到7．58g／cm^3，接近材料的理论密度，同时磁体的尺寸精度达到20μm。     

烧结温度对稀土永磁Sm(Co0.72Fe0.15Cu0.1Zr0.03)7.5的磁性能的影响

采用粉末冶金法制备稀土永磁Sm(Co0.72Fe0.15Cu0.1Zr0.03)7.5,研究烧结温度对磁体的磁性能的影响.结果表明:随着烧结温度的提高,剩磁Br、内禀矫顽力Hci及最大磁能积(BH)max都先增加后降低.虽然Br在烧结温度为1220℃时获得最大值0.95T,但磁体的综合磁性能在烧结温度为1215℃时最优,Br、Hci和(BH)max分别达到0.94T、2276.6kA·m-1和171.9kJ·m-3.1215℃烧结的磁体的温度稳定性较好,有望应用到550℃环境中.     

放电等离子烧结NdFeB永磁材料的矫顽力研究

利用VSM,对放电等离子烧结NdFeB磁体磁化和退磁过程及不同磁化场下的约化矫顽力与外场角度关系进行了研究,发现样品在外场作用下,磁畴壁被钉扎的特征;利用SEM的电子能谱研究了热处理过程对样品矫顽力的影响.结果表明SPS NdFeB的矫顽力机制属于钉扎类型.     

放电等离子烧结NdFeB磁体的磁化特征

利用放电等离子烧结技术(SPS)制备烧结钕铁硼磁体SPS NdFeB。为了更好地理解SPS Nd-FeB磁体的磁硬化机理,利用振动样品磁强计研究了SPS NdFeB磁体在室温下的磁化和反磁化过程。结果表明,在强度为800kA/m的较低外加磁场和强度为1760kA/m的较高外加磁场下的磁化特征明显不同,前者可称为形核控制模式,后者则为钉扎控制模式。比较样品的磁化过程和反磁化过程的曲线,发现样品的矫顽力大小等于样品磁化过程钉扎场的大小。     

NdFeB/酚醛树脂原位复合材料研究

采用原位聚合法制备了NdFeB/酚醛树脂(PF)母料,并进一步制备了粘结磁体.采用红外分析了NdFeB/PF母料的结构,并用多种方法对粘结磁体的磁性能和力学性能进行了研究.研究表明:在原位制备过程中,PF的聚合倾向于在NdFeB的表面进行,形成PF包覆的NdFeB,NdFeB磁粉进入了PF的生成体系,形成了海岛结构.比较三种工艺制备的磁体综合性能可知,采用NdFeB/PF母料粉料作粘结剂制备的磁体的综合性能最好.     

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.