Densification and microstructure evolution during SPS consolidation process in W-Ni-Fe system

Spark plasma sintering method （SPS） was used to consolidate mixed W-5.6Ni-1.4Fe （mass fraction, %） powders from commercial fine elemental powders, and both the densification behavior and microstructure evolution in sintering were investigated at different heating rates. The results show that the SPS densification process can be divided into three stages. At the initial unshrinking stage, fast heating generates instantaneous discharge and locally inhomogeneous temperature distribution in solid-state powder particles, enhancing later densification; during the intermediate solid state sintering stage, diffusion is more sufficient in the slow-heated SPS process; at the final transient liquid-phase sintering stage, tungsten grains become sphered and coarsen rapidly, but fast heating helps maintain rather small grain sizes.

Thermodynamic Properties of Nanograin Boundary and Thermal Stability of Nanograin Structure

The thermal features of the nanograin boundary were described by a developed thermodynamic model. Using the nanocrystalline Cu as an example, the pressure, the bulk modulus, and the volume thermal expansion coef- ficient were calculated to characterize the thermodynamic properties of the grain boundaries on the nanoscale. Based on the parabola-type relationship between the excess free energy and the excess volume of the nanograin boundary, the thermal stability, as well as its evolution characteristics, was analyzed. The experimental re- sults of the temperature-varying grain growth in the nanocrystalline Cu, which exhibited the discontinuous nanograin growth behavior, verified the thermodynamic predictions. In addition, the quantitative relationships correlating the excess volume and the lattice expansion with the nanograin size were discussed.

Microstructure and mechanical properties of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy sintered at different SPS temperatures

TiAl alloy bulk samples with the composition of Ti-45Al-5.5(Cr,Nb,B,Ta) (mole fraction, %) were prepared by high energy mechanical milling and spark plasma sintering (SPS) and then heat treatment. The microstructure and mechanical properties after heat treatment of TiAl alloy prepared by SPS at different temperatures were studied. The results showed that the morphology of high energy mechanically milled powder was irregular and the average grain size was about decades micrometers. X-ray diffraction analysis showed that the mechanically milled powder was composed of two phases of TiAl and Ti3Al. The main phase of TiAl and few phases of Ti3Al and TiB2 were observed in the SPS bulk samples of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy. For samples sintered at 900 °C and 1000 °C, the microstructure was duplex structure with some fine equiaxed gamma grains and thin needly TiB2 phases. With the SPS temperature increasing from 900 °C to 1000 °C, the micro-hardness was changed little, the compression strength increased from 1812 MPa to 2275 MPa and the compression ratio increased from 22.66% to 25.59%. The fractography results showed that the compression fracture transform of the SPS Ti-45Al-5.5(Cr,Nb,B,Ta) alloy was rgranular rupture.

Microstructure characteristics and mechanical properties of TiB/Ti-1.5Fe-2.25Mo composites synthesized in situ using SPS process

TiB/Ti-1.5Fe-2.25Mo composites were synthesized in situ using the spark plasma sintering （SPS） method at temperatures of 850-1150 °C. The effect of the sintering temperature on microstructure and mechanical properties of the composites was investigated. The results indicate that the aspect ratio of the in situ synthesized TiB whiskers in Ti alloy matrix decreases rapidly with an increase in sintering temperature. However, both the relative density of the sintered specimens and the volume content of TiB whiskers in composites increase with increasing sintering temperature. Thus, the bending strength of the composites synthesized using SPS process increases slowly with increasing the sintering temperature from 850 to 1150 °C. TiB/Ti-1.5Fe-2.25Mo composite synthesized at 1150 °C using SPS method exhibits the highest bending strength of 1596 MPa due to the formation of fine TiB whiskers in Ti alloy matrix and the dense microstructure of the composite.

High-dielectric-constant nanograin BaTiO_(3)-based ceramics for ultra-thin layer multilayer ceramic capacitors via grain grading engineering

Four BT-based ceramic samples were prepared using a grain grading approach.The bigger-grained(~100 nm)and smaller-grained(~70 nm)BaTiO_(3)(BT)powders were mixed.The smaller-grained BT powder controlled the average grain size and guaranteed the reliability,while the bigger-grained powder enhanced the dielectric constant.Various percentages of bigger-grained BT powder were introduced to balance the average grain size and the dielectric constant.As the proportion of bigger grains increased,the dielectric constant(εr)improved significantly.The room-temperatureεr of 25%bigger-grain mixed BT(2623)was~50%higher than that of the sample with a similar average grain size without grain grading.The ceramic mixed with 15%bigger-grained BT showed comprehensive dielectric performance,which met the EIA X5R standard and provided a considerableεr of 1841 along with a low dielectric loss of 0.78%.Notably,the average grain size was 90 nm,which favors the applications in ultra-thin multilayer ceramic capacitors.

Influence of the C-S-H Amount on [Cl^-]/[OH^-]Ratio of Simulated Concrete SPS and the Corrosion Susceptibility of Steel

Two kinds of simulated concrete pore solutions（SPSs） were treated with different amounts of synthetic calcium silicate hydrate（C-S-H）. The variation of the [Cl^-]/[OH^-] ratio in SPS was measured and the corrosion susceptibility of carbon steel in the SPS was investigated with potentiodynamic polarization, EIS and weight lose tests. The experimental results showed that for the SPS at p H 12.5, as the amount of C-S-H increases, the [Cl^-]/[OH^-] ratio increases thereby causing an increase in the corrosion susceptibility of the steel. While for the SPS at p H 9.7, with increasing C-S-H amount, the drop amplitudes of both [Cl^-]/[OH^-] ratio and steel corrosion rate first decrease and then increase, and a 3% C-S-H addition shows the best inhibition effect. XPS results demonstrate that after C-S-H treating in p H 12.5 SPS the [Fe^（3＋）]/[Fe^（2＋）] ratio in the film on steel surface is reduced while in p H 9.7 SPS the [Fe^（3＋）]/[Fe^（2＋）] ratio is increased. The different effects of the C-S-H amount on the two SPSs and the steel corrosion behavior result from the influences of C-S-H on the SPS p H, which is related to the composition of the SPS.

Fabrication of Transparent Polycrystalline Yttria Ceramics by Combination of SPS and HIP

Transparent polyerystalline yttria is a promising optical ceramics with excellent physical and chemical properties. A commercial yttria powder with a mean particle size of 1.0μm and narrow size distribution was selected as the starting material. Transparent polyerystalline yttria ceramics without any additives were successfully prepared by hot isostatic pressing (HIP) at 1700℃for 2 h under the pressure of 200 MPa in Ar following spark plasma sintering (SPS). The as-prepared specimens consist of uniform grains of ~ 40μm. Scanning electron microscopy (SEM) images show their pore-free structure. The influences of the yttria powder and sintering process on the properties of the yttria ceramics, including the microstructure and optical properties, were further investigated in our study.

SPS东南大学分会喜获2012 SPS Undergraduate Research Award

日前，一年一度的SocietyofPhysicsStudents（简称SPS）学会本科生科研奖项：Un—dergraduateResearchAward在全球范围内展开评选，本次全球共选出了九个研究项目．其中，由SPS东南大学分会会员刘雨露、金天晨、刘继龙和刘奇同学，在物理系倪振华教授的指导下，申报的ControlledGrowthofGraphenebyCheroicalVaporDeposition（石墨烯的CVD控制合成）研究项目摘得该奖项，获得SPS美国总部1900美元的研究经费支持．

从SN388 SPS的应用效果看仪器新技术的研究与开发

SPS应用于地震勘探中有诸多好处,能简化工作,节约时间,并能实时监控野外生产过程,从而有效保障采集质量。本文详细介绍了SN388仪器运用此技术在塔里木施工的有关情况,取得的效果良好。本文作者由此还提出:仪器新功能的研究与开发需要技术人员全方位的参与。

Numerical Simulation of the Temperature Field in Sintering of TiB_2-BN by SPS

The temperature field during the whole process of SPS sintering TiB2 -BN sample was numerically simulated based on the simplification of the temperature rising process. The result shows that the highest temperature is found in the punch and the heat flows from punch to sample and die in SPS sintering system. In the radial direction, the center temperature of the sample is much higher than the circumference temperature of the sampie. In the axial direction, the center temperature of the sample is lower than the border temperature of the sampie. The temperature difference in the sample is growing bigger in the sintering process and reaches the maximum at the end of the heating-up process.

TD-SCDMA HSPA+ CPC E-DCH SPS初始链路适配技术探讨

随着TD-SCDMA网络的商用,鼎桥现网设备基本支持HSPA,并从硬件上支持HSPA+功能。在TD-SCDMA现网的HSPA典型配置中,用户基本会配置上下行伴随信道(ADPCH),从而导致系统的接入用户数受到ADPCH码道数的限制。在HSPA+连续分组连接(CPC)技术中,信道配置可以取消上下行伴随信道,通过配置使用E-DCH半持续调度(SPS)资源传送上行信令或数据,从而取消了上行ADPCH码道限制。本文在分析CPCE-DCH半持续调度技术的基础上,通过终端接入时的接收信号码功率(RSCP)信息上报,基站的MAC-ehs根据上行时隙的干扰、终端的路损信息、终端能力和网络资源使用情况,初始适配终端的链路质量,计算分配给终端的初始E-DCH半持续调度资源,从而减少采用固定方式分配初始E-DCH半持续调度资源导致初始授权分配不准确,后续需要通过E-AGCH重配置E-DCH半持续调度资源的可能性,提高E-AGCH的利用率和系统性能。

Two-step Synthesis of TiC_(0.7)N_(0.3)@WC-MoC_2 Core-shell Microspheres and Fabrication of TiC_(0.7)N_(0.3)@WC-MoC_2-based Cermets by SPS

The precursor with TiC0.7N0.3@WO3-MO3 microspheres were prepared by a novel method from the WO3-MoO3 sol dipping. Subsequently, TiC0.7N0.3@WC-MoC2 core-shell structural microspheres were successfully obtained by carburizing the precursor at 900 °C in a flowing mixture of CH4 （20 ml·min-1） and H2 （200 ml·min-1） for 2 h. Then TiC0.7N0.3@WC-MoC2-15Co cermets were prepared utilizing the core-shell powders by spark plasma sintering （SPS）. Powders of the precursors with TiC0.7N0.3@WO3-MO3 microspheres, TiC0.7N0.3@WC-MoC2 microspheres and TiC0.7N0.3@WC-MoC2-15Co cermets were characterized by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）. The obtained TiC0.7N0.3@WC-MoC2 microspheres have a dense WC-MoC2 coatings shell. The thickness of the shell could be easily controlled by adjusting the number of sol dipping cycles. It was found that the TiC0.7N0.3@WC-MoC2 microspheres were more beneficial to fabricate the ＂core-rim＂ structures by SPS.

A Hybrid Simulation Test Platform for Verifying the Protection Settings of SPS

To verify the effectiveness and correctness of the protection settings in ring structure Shipboard Power System (SPS), a digital-physical hybrid simulation platform at China Ship Development and Design Center (CSDDC) has been built, which aims to give double verification effect of design scheme and physical device. The platform consists of eMEGAsim digital simulator, signal power amplifiers and digital-analog interface equipments. With this platform, the multiple protection device of ring structure grid can be accessed to form a close-loop test system. Since eMEGAsim model-simulated faults and actual protection device actions are on real time, the tripping settings of each device as well as their coordinate performance between multiple devices can be verified in this close-loop test.

Mechano-Synthesized Orthoferrite Starting from Wüstite Assisted by SPS

Stoichiometric mixtures of FeO and Y2O3 were milled and heat treated to obtain yttrium iron garnet, Y3Fe5O12. Two types of heating systems were used: one, a spark plasma sintering machine and the second, an electrical oven. The magnetic properties of the resulting specimens have been analyzed and discussed as a function of the grain size and the particles’ morphology. The partial formation of garnet and orthoferrite phases was revealed on the obtained powder through microstructural analyses after 9 h of ball milling. The milled powders were transformed into the orthoferrite phase after the SPS-treatment at 700°C and 900°C. Magnetic-saturation studies revealed magnetic responses up to 12.7 emu/g for specimens SPS-treated at 700°C, whereas 2.1 emu/g for samples SPS-treated at 900°C. Conventionally treated specimens at 700°C developed 0.36 emu/g of magnetization, while 0.93 emu/g was registered for those treated at 900°C.

Playing Catch-up China’s Agricultural Produce Exports Struggle under the WTO’s SPS Agreement

THE World Trade Organization＇s Agreement on the Application of Sanitary and Phytosanitary Measures, also known as the SPS Agreement, stipulates guidelines relating to bacterial contaminants, pesticides, inspection and labeling of member states＇ food imports, and aims to stop the transnational spread of pests and diseases.

Research on dynamic response characteristics of CFRP/Al HC SPs subjected to high-velocity impact

CFRP/Al HC SPs(Carbon Fiber Reinforced Plastic/Aluminum Honeycomb Sandwich Panels)composite structures are widely used in the aerospace and many other fields due to their excellent performances. In order to reveal profoundly the dynamic response characteristics of CFRP/Al HC SPs composite structure under high-velocity impact loading, the experiments about aluminum honeycomb core and CFRP/Al HC SPs composite structure impacted by high-velocity projectiles have been performed by using a one-stage light gas gun loading and a high-speed camera systems, respectively. The whole physical process of collision is analyzed by using TEMA software which is provided by high-speed camera's manufacturer,and the pictures and related physical parameters of the projectile passing through the different layers at the key moments are extracted based on the set frame rate of the video. Meanwhile, the ABAQUS/Explicit module was used to conduct numerical simulation under the same conditions as the experiments, and extracting the pictures and related physical parameters during the projectile penetrating through aluminum honeycomb core and the sandwich panels at the different key moments. The results show that the durations of action for the projectile impacting the Al HC core and the CFRP/Al HC SPs at the velocity about 280 m/s were 86 μs and 240 μs in experiments, respectively, and the durations of action were 90.7μs and 236.2 μs at the same experimental conditions in numerical simulation, which were basically consistent comparing the experimental to simulated results. Moreover, more than 70% for the kinetic energy of the projectile consumed by the sandwich panels was attributed to the front panel and the aluminum honeycomb core during the entire impact process, and all these have verified the reliability of the numerical simulation.

Applying the SPS Agreement to Protect National Ecological Safety

With the release of the National Programof ecological and environmental protection inrecent years,the ecological security in our countryhas become a strategic choice for the new century.However,in recent years,biodiversity has faced aserious threat that accelerates species extinctionand ecosystem degradation,which has aggravatedthe crisis we now face.The invasion of alienspecies into the ecological environment has becomethe main cause of biodiversity loss.

Microstructure,Properties,and Grain Growth Kinetics of Mo-5Ta Refractory Sputtering Targets Prepared by SPS

Mo-5Ta targets were prepared by the spark plasma sintering(SPS)technology under the sintering temperatures of 1400-1600℃,the holding times of 0-20 min,and the axial pressure of 30 MPa.The microstructure,performance,and grain growth kinetics of Mo-5Ta sputtering targets were studied.With the increase of sintering temperatures and times,Ta can more dissolve in Mo and form a Mo(Ta)solid solution.The grain sizes of Mo-5Ta targets remain unchanged at low temperatures(1400-1500℃)while increasing significantly at high temperature(1600℃)with the extension of the holding time.In addition,the densities and Vickers hardness(HV_(0.5))first ascend and then decrease with sintering proceeding.The thermal conductivity is positively correlated with the grain size and density,as a result of their joint action.Based on the comprehensive analysis,the grain growth is dominated by the combination of boundary diffusion and volume diffusion.When n=2,the activation energies of grain growth under holding times of 5,10,20 min are calculated as 762.70,617.86,and 616.52 kJ/mol,respectively.