In-situ observation of porosity formation during directional solidification of Al-Si casting alloys

In-situ observation of porosity formation during directional solidification of two Al-Si alloys (7%Si and 13%Si) was made by using of micro-focus X-ray imaging.In both alloys,small spherical pores initially form in the melt far away from the eutectic solid-liquid (S/L) interface and then grow and coagulate during solidification.Some pores can float and escape from the solidifying melt front at a relatively high velocity.At the end of solidification,the remaining pores maintain spherical morphology in the near eutectic alloy but become irregular in the hypoeutectic alloy.This is attributed to different solidification modes and aluminum dendrite interactions between the two alloys.The mechanism of the porosity formation is briefly discussed in this paper.

Solidification process of conventional superalloy by confocal scanning laser microscope

The solidification process of a conventional superalloy, IN718, was investigated by confocal scanning laser microscope （CSLM）. The liquid fraction during solidification was obtained as a function of real time and temperature in reference with the in-situ observation. The characteristics of L→γ transformation were analyzed and the γ growing rate of each stage was also calculated. Scheil equation was employed to predict the segregation behavior, and the predict results are in consistence with the experimental results. As a result, the confocal scanning laser microscope shows a great potential for solidification process research.

A review of solid-state lithium metal batteries through in-situ solidification

High-energy-density lithium metal batteries are the next-generation battery systems of choice,and replacing the flammable liquid electrolyte with a polymer solid-state electrolyte is a prominent conduct towards realizing the goal of high-safety and high-specific-energy devices.Unfortunately,the inherent intractable problems of poor solid-solid contacts between the electrode/electrolyte and the growth of Li dendrites hinder their practical applications.The in-situ solidification has demonstrated a variety of advantages in the application of polymer electrolytes and artificial interphase,including the design of integrated polymer electrolytes and asymmetric polymer electrolytes to enhance the compatibility of solid–solid contact and compatibility between various electrolytes,and the construction of artificial interphase between the Li anode and cathode to suppress the formation of Li dendrites and to enhance the high-voltage stability of polymer electrolytes.This review firstly elaborates the history of in-situ solidification for solid-state batteries,and then focuses on the synthetic methods of solidified electrolytes.Furthermore,the recent progress of in-situ solidification technology from both the design of polymer electrolytes and the construction of artificial interphase is summarized,and the importance of in-situ solidification technology in enhancing safety is emphasized.Finally,prospects,emerging challenges,and practical applications of in-situ solidification are envisioned.

Growth mechanism of reinforcements in in-situ synthesized (TiB+TiC)/Ti composites

The growth mechanism of reinforcement in in situ synthesized (TiB+TiC)/Ti composites was investigated. The results show that reinforcements nucleate and grow in a way of dissolution precipitation. The morphologies of reinforcements are closely related to the solidification paths and crystal structure of reinforcements. TiB, as a reinforcement, is liable to grow along [010] direction and forms in short fibre shape due to its B27 structure, whereas primary TiC is liable to form composition undercooling and grow in dendritic shape. TiC phases precipitated in binary eutectic and ternary eutectic reactions grow in equiaxial shape. The addition of aluminum element refines TiB and TiC particles, and makes TiC reinforcements grow into the equiaxial particles easily. The addition of graphite adjusts the solidification paths and forms more TiC with dendritic shape. [

In-situ composite Cu-Cr contact cables with high strength and high conductivity

In order to develop a new type of contact cable with high strengthand high electrical conductivity, Cu-Cr alloy series were selected asmaterials and cu-Cr alloy castings were produced by means ofdirectional solidification continu- ous casting (DSCC) process. theresults show that the fibrillar strengthening phase, β-Cr, orderlyarranges among the copper matrix phase along the wire direction; andmicrostructure of in-situ composite forms, which retains the basicproperty of good conductivity of the copper matrix and meanwhileobtains the strengthening effect ofβ-Cr phase.

In-situ observation of solid-liquid interface transition during directional solidification of Al-Zn alloy via X-ray imaging

The morphological instability of solid/liquid(S/L)interface during solidification will result in different patterns of microstructure.In this study,two dimension(2 D)and three dimension(3 D)in-situ observation of solid/liquid interfacial morphology transition in Al-Zn alloy during directional solidification were performed via X-ray imaging.Under a condition of increasing temperature gradient(G),the interface transition from dendritic pattern to cellular pattern,and then to planar growth with perturbation was captured.The effect of solidification parameter(the ratio of temperature gradient and growth velocity(v),G/v)on morphological instabilities was investigated and the experimental results were compared to classical"constitutional supercooling"theory.The results indicate that 2 D and 3 D evolution process of S/L interface morphology under the same thermal condition are different.It seems that the S/L interface in 2 D observation is easier to achieve planar growth than that in 3 D,implying higher S/L interface stability in 2 D thin plate samples.This can be explained as the restricted liquid flow under 2 D solidification which is beneficial to S/L interface stability.The in-situ observation in present study can provide coherent dataset for microstructural formation investigation and related model validation during solidification.

Solidification behaviour and hot cracking susceptibility of a novel Ni-based superalloy

A novel Ni-based superalloy GH4151,with a γ′ volume fraction of about 55%and a service temperature capability up to 8oo oC,was investigated.Due to the different cooling conditions of various regions during the solidification of ingots,significant cooling rate variations may lead to the occurrence of hot cracking.Conventional scanning laser microscope was utilised to investigate the solidification process and phase precipitation behaviour of the GH4151 under wide range cooling rates.The characteristics of L→γ transformation were analysed,and the growth rates of at each stage were calculated.The segregation behaviour was predicted using the Scheil equation,and the predicted results match well with the experimental results.The sensitivity coefficient for hot cracking was modified,and cracking sensitivity coefficient values for the alloy under different cooling rates were computed,revealing that the alloy is most susceptible to hot cracking at 10℃/min cooling rate.Therefore,controlling the cooling rate can reduce the possibility of hot cracking in ingot.

原位固化技术在超深淤泥浅层处理中的应用

超深淤泥地基因其流塑性强、承载力低的特点,对其进行处理往往存在工期长、造价高、易失稳的问题。为完善现有超深淤泥地基处理方法,特别是相关理论计算存在的不足,该文以第十一届江苏园博园城市展园泥潭绿色改造为工程背景,针对性提出超深淤泥地基浅层原位固化处理方案。对原位固化桩复合地基的承载力和沉降计算进行了详细分析,梳理了完整的计算流程,并通过现场载荷试验,进一步验证了该方案实施的可行性,可为同类工程提供技术参考。

Microstructural Evolution and Performance of In-situ Ag-Ni Composite after Solidification under Electromagnetic Stirring and Deformation

The effect of electromagnetic stirring（EMS）on microstructure and performance of Ag-8 mass%Ni composite was investigated under both solidified and deformed conditions.Without EMS,the Ag matrix formed short,thick dendrites in the ingot;whereas with EMS,dendrites were long and slim.Ni phase mainly formed particles or ribbons,distributed along boundaries between dendrite arms.Cold drawing of the solidified Ag-Ni ingots,both with and without EMS,produced high strength in-situ metal-matrix composite（MMC）consisting of Ag matrix reinforced by Ni ribbons.EMS improved the ductility of the composite,consequently enhancing its drawability and strength.EMS also increased the electrical conductivity in both solidified ingots and deformed in-situ composite wires.In both cases,hardness and tensile strength remained high.A model based on a combination of the modified linear rule of mixtures and the Hall-Petch relationship was used to rationalize the tensile strength and hardness with respect to its fabrication parameters and the microstructure of Ag-Ni in-situ composite.

Heat transfer behavior of AZ80-1%Y alloy during low-frequency electromagnetic casting

Heat transfer behaviors of AZ80?1%Y alloy during low frequency electromagnetic casting (LFEC) and direct chilling casting were studied by in-situ temperature measurement. The results demonstrated that the low frequency electromagnetic field (EM) caused forced convection in the melt during LFEC. The forced convection led to uniform solidification velocity and temperature field. EM frequency, excitation current intensity and casting temperature could control the heat transfer behavior. The forced convection could improve the microstructure and degrade the difference in microstructure between the edge and center of billet. Appropriate parameters of low frequency EM for casting Mg alloy are 20 Hz of frequency and 60 A of electric current intensity.

路堤荷载下浅层就地固化联合管桩复合地基桩-土应力比及沉降计算

浅层就地固化联合管桩复合地基是超软土地基加固的有效方法之一。基于复合地基荷载传递法理论,将路堤填料、固化层、基桩、桩间土和下卧层作为一个系统,建立考虑应力、沉降变形连续性的浅层就地固化联合管桩复合地基的理论计算方法,探讨浅层固化层对管桩复合地基桩-土应力比及地基沉降的影响规律。通过与浅层就地固化联合管桩复合地基现场试验结果的比较分析,并与传统管桩复合地基现场试验结果对比,验证了所建立的理论计算方法的准确性和可靠性。研究结果表明,浅层固化层的设置能够充分发挥管桩复合地基中基桩的承载性能,桩-土应力比随着浅层固化层模量的增大而呈线性增加(斜率约为1.6MPa^(-1));现场工况下,桩体中性点位置随浅层固化层模量的增大而上移(介于0.12~0.45之间);考虑到发挥固化剂材料性能及加固效果,选取水泥掺量不超过11%的固化剂较为合适。

道路工程深厚淤泥软土地基处置关键技术研究

为了提高道路修建所遇到的深厚软土地基承载力,保证道路运行时路堤稳定性,需要优化深厚软土地基施工技术。本项目拟以温州玉环市深厚软土地基市政道路修建工程为研究对象,通过就地浅层固化处理方法提高地基强度,完成深厚软土地区道路工程修建。施工结果表明,施工后道路沉降监测点位的沉降位移均低于规范允许沉降位移,采取的就地浅层固化软基处置方案效果较好,符合后续的施工需求,对完善区域交通路网发展具有重要意义。

鱼塘路段人工硬壳层承载特性及计算方法

常规的鱼塘路段的处理均采用换填法,为避免淤泥运出和填筑材料的制作过程中对环境产生的不利影响,采用软土就地固化技术改良鱼塘底部淤泥。首先介绍就地固化设备,并以潮汕环线高速公路就地固化试验段工程为例,详细介绍该技术在鱼塘路段的应用及其优势。现场试验结果表明:固化28 d后表层承载力能满足要求,搅拌不均匀现象对承载力影响较大,并得到固化土承载力与深度的关系。结合现场试验与相关资料,评价了部分承载力判断方法,推导得到适用于就地固化检测的N_(63.5)-f_(a)曲线拟合公式。

钢渣型复合基材在浅层软土固化中的应用

浅层就地固化是软土地基处理的一项重要方向,近年来在工程建设中得到较为广泛的应用。传统就地固化主要以水泥为主,为了验证基于工业废料钢渣的复合系基材对不同软土地区浅层固化的效果,通过改变钢渣、偏高岭土、生石灰等成分的配比,在室内以无侧限抗压强度为指标,探讨不同成分配比的基材对不同地区软土固化强度随含水率、复合基材掺量和龄期变化的影响;此外,将室内试验最优配比应用于现场试验,在现场通过取芯测强度以及轻便动探评价承载力来验证复合基材对于浅层软土就地固化的效果,并对室内和现场所造成的强度差异进行了对比分析。研究结果表明:①基于钢渣的复合系基材能有效提高软土强度:②固化后强度与基材掺量、龄期成正相关关系,与含水率成负相关;③在浙江湖州现场就地固化中,复合基材掺量大于3%,改性水泥与钢渣掺量比为1.2∶1.8时,可满足固化土强度和地基浅层承载力的要求;④现场搅拌均匀性是影响室内与现场强度差异的主要原因。

In-situ study on nutrient release fluxes from shallow lake sediments under wind-driven waves

An in-situ benthic device to measure nutrient fluxes across the sediment-water interface has been developed and successfully used to study both static and dynamic fluxes of nutrients in Dianshan Lake, China. The result shows that the surface sediments of Dianshan Lake were resuspended under wind-driven waves. DOC entered into overlying water only when sediments were resuspended. The average DOC flux was 105.78 mg/（mEd）, while the static and dynamic POC fluxes were 48.22 mg/（mEd） and 10 273.20 mg/（m2d）, respectively. Ammonia and nitrate had no significant release, and the dynamic flux of TN was 87.11 mg/（m2d）. The release of phosphorus was the most evident, and the dynamic fluxes of SRP and DTP were 20.22 mg/（m2d） and 21.78 mg/（mEd）, 2.2 and 2.0 times higher than the static fluxes, respectively. Dissolved phosphorus was released mainly as SRP, and phosphorus release from the sediments in Dianshan Lake cannot be ignored.

Behavior of Inclusions in Process of Solid Growth During Solidification of Fe-0.15C-0.8Mn Steel

The behavior of inclusions in the process of B-phase growth during the solidification of Fe-0.15C-0.8Mn steel was in-situ observed using a high-temperature confocal scanning laser microscope （HTCSLM）. The results show that inclusions arrive the S/L （solid/liquid） interface by way of direct impact or gradual drift, when the ceil spacing is approximately equal to 177 um during the growth of cellular B-phase. The inclusions easily stay at the positions of trailing vortex formed by the circumferential motion of molten steel around B-phase. Some inclusions reaching the S/L interface are captured by the solid-phase. Some of them move along the normal direction of the S/L in- terface because of pushing of solid-phase, and the others get away from the S/L interface after being pushed for a distance. The faster the growth rates of the solid-phase are, the easier the inclusions are captured by the S/L interface. The slower the growth rates of the solid-phase are, the easier the inclusions move with the S/L interface.

人工硬壳层对于既有管道的影响特性研究

上海金海公路改建工程中老路堤侧存在既有管道和明浜,明浜的存在给施工带来了较大的困难。因此,提出了软土就地固化技术,代替传统换填方案,极大地加快了施工进度。明浜软土固化后,经荷载板试验检测极限承载力可达336 kPa,十字板剪切试验测试其剪切强度最大可达386.4 kPa,处理后表层压实度可达90%。通过有限元计算模型开展了人工硬壳层对于既有管道的应力和变形影响规律研究,发现经过应力扩散后管道上覆应力减少约15%,相比于传统换填施工方案,管道沉降可减少2%,路堤中心沉降可减少2.4%。人工硬壳层不仅能够快速处理明浜区域,也能够有效降低既有管道的上部荷载,具有控制沉降、保护管道的作用,可为工程中类似问题提供参考。

铁路浅表层淤泥地基固化试验研究

选用无机粉态和液态固化剂配以硅酸盐水泥对浅表层淤泥土进行固化,通过宏观静力学试验和动三轴试验以及微观扫描电镜分析,进行铁路浅表层淤泥地基固化研究。结果表明:液态固化剂在固化施工和提高淤泥土性能上优于粉态固化剂,固化剂掺量相同时,液态固化剂固化淤泥土强度高于固态固化剂,掺量在3%~4%时高出30%以上;固化淤泥土在14d后强度趋于稳定;淤泥土在循环动载作用下的动应变随水泥和固化剂含量的增加而大大减小,水泥或固化剂掺量增加2%,在50N动荷载下减小约2倍,在100N动荷载下减小3~5倍;淤泥土的动弹模随水泥掺量和固化剂掺量的增加略微增大;淤泥加固后原状土的粒状架空结构中颗粒间缝隙被填充,结构更加密实,因此宏观动强度增大。

就地浅层固化技术稳定性与可靠性研究

就地浅层固化技术是一种环保、经济型加固处理软弱土体工艺,近年来虽然其已被大量应用于处理道路路基明浜和暗浜,但是关于该工艺的应用性研究成果并不多,稳定性与可靠性方面研究更少。因此,以昆阳路越江及配套道路工程和S3公路新建工程为载体,在采用相同工艺、材料和配合比条件下,开展该技术工艺固化稳定性和可靠性研究。研究结果表明:经就地浅层加固处理后,两个工程道路路基承载力均满足设计要求,而且最大沉降量、最大回弹量及回弹率等检测参数的数值大小与分布区间比较窄而稳定。

珠海某深厚软土浅层地基固化处理措施方法

珠海市位于珠江三角洲,广泛分布着三角洲相软土,如不进行地基处理,大型施工设备无法直接行走、作业。由于传统的堆载预压处理方法所需时间较长,无法满足工期需要,因此对于有工期要求的工程,需要一种较快速的处理方式。结合珠海某管桩基础工程实例,介绍了一种软土浅层地基固化处理方式,通过处理后抽芯、管桩机行走作业,验证了其处理效果。其相较传统堆载预压处理方法不但具有工期短的特点,并且地基经处理后具有防止管桩偏位,避免承台开挖时发生淤泥翻涌现象的优点,为此类地质条件的工程提供参考。