Phase-field simulation of dendritic solidification using a full threaded tree with adaptive meshing

Simulation of the microstructure evolution during solidifi cation is greatly benefi cial to the control of solidifi cation microstructures. A phase-fi eld method based on the full threaded tree(FTT) for the simulation of casting solidifi cation microstructure was proposed in this paper, and the structure of the full threaded tree and the mesh refi nement method was discussed. During dendritic growth in solidifi cation, the mesh for simulation is adaptively refi ned at the liquid-solid interface, and coarsened in other areas. The numerical results of a threedimension dendrite growth indicate that the phase-fi eld method based on FTT is suitable for microstructure simulation. Most importantly, the FTT method can increase the spatial and temporal resolutions beyond the limits imposed by the available hardware compared with the conventional uniform mesh. At the simulation time of 0.03 s in this study, the computer memory used for computation is no more than 10 MB with the FTT method, while it is about 50 MB with the uniform mesh method. In addition, the proposed FTT method is more effi cient in computation time when compared with the uniform mesh method. It would take about 20 h for the uniform mesh method, while only 2 h for the FTT method for computation when the solidifi cation time is 0.17 s in this study.

Experimental research on solidification structure of alloy 800H by linear electromagnetic stirring

The solidifi cation structures of alloy 800 H fabricated with and without linear electromagnetic stirring(L-EMS) were investigated. The results show that the solidification structure of the alloy can be obviously affected by the forced convection in melt caused by L-EMS. The average size of equiaxed grains of the alloy with L-EMS decreases from 3.5 mm to 2.3 mm, and the ratio of equiaxed grain increases from 5% to 43% compared with that without L-EMS. The microstructure of the alloy without L-EMS is composed of f ine equiaxed dendrites in the outermost layer and columnar dendrites in other areas, whereas that with L-EMS contains equiaxed dendrites, columnar dendrites and cross dendrites. In addition, the mechanism of dendrite fragment drift was proved by examining the composition change of the main alloying elements in the dendrite trunks at different solidifi cation stage using an electron probe micro-analyzer(EPMA).

Effect of abruptly changing withdrawal rate on solidification microstructure in directionally solidified Al-4.5wt%Cu alloy

Al-4.5wt.%Cu alloy has been directionally solidified at constant and abruptly changing withdrawal rates, respectively. The effects of the withdrawal rate on solidification microstructure, primary dendrite arm spacing(PDAS) and liquid solute distribution in front of the solid-liquid interface were investigated. The experimental results for the PDAS at a constant withdrawal rate agree well with the values calculated by the Hunt, Trivedi and Hunt-Lu models. At an abrupt change in the withdrawal rate, the maximum to minimum ratio of the PDAS at a given solidification parameter, i.e. λ1max/λ1min, is more than 2, and the PDAS values are remarkably history-dependent. Further, the liquid-solute distribution curve based on theoretical calculation shows that the larger the initial withdrawal rate is, the smaller the minimum of liquid solute concentration in front of the solid-liquid interface is after the abrupt change in withdrawal rate.

Casting of aluminum-copper based alloy by controled difusion solidiication

A quaternary alloy(Al-5.0Cu-0.35Mn-0.25Ti, wt.%), having a similar chemical component with ZL205A, was prepared using a controlled diffusion solidification(CDS) process and a conventional casting process. The effect of the casting process on microstructure and hardness was investigated. The grain morphology and casting defects of the alloy prepared via the conventional casting and CDS were observed and compared at various pouring temperatures. Results show that the CDS process can alleviate the hot tearing defects and reduce the density of porosity, while getting rid of the riser that is generally used for feeding during conventional casting. Structure observations show that the grain morphology of the conventional cast alloy is mainly dendritic, and the grain size decreases when the pouring temperature is decreased, while the CDS cast alloy consists of a large number of spherical grains, which can decrease the thermal cracking tendency and segregation defect, and enhance the hardness of the alloy.

扶余油层采出液特性及集输参数界限研究

杏北扶余油层属低孔、特低渗透储层,采出液呈现高凝、高黏的特点,为确保原油稳定集输,转油站掺水温度高,单井掺水量大,集输单耗高。通过开展扶余采出液特性研究,明确了扶余采出液性质,与常规萨葡高油层相比,扶余油层采出液黏度及凝固点高,乳化油粒径小、稳定性强,导致集输与处理困难大。通过开展掺水优化现场试验,确定了扶余油井能耗最佳运行参数,以凝固点为集输进间边界,有效降低集输能耗,为后续区块规划设计及低耗运行提供指导依据。

Fabrication of lotus-type porous micro-channel copper by single-mold Gasar technique

A single-mold Gasar technique was developed to produce lotus-type porous micro-channel copper with uniform porous structure. In this paper the effect of withdrawal rate on the solid/liquid interface morphology and the corresponding porous structure was systematically investigated, especially the pore morphology, pore growth direction, porosity, and pore diameter of porous copper ingots. In addition, a temperature fi eld simulation was carried out based on Pro Cast software to investigate the shape and movement velocity of the solidifying solid/liquid interface. The experimental results show that the solidifi cation interface changes from convex to planar, then to concave shape with an increase in withdrawal rate. The average porosities of copper ingots are constant and independent of the withdrawal rate. The average pore diameter decreases with an increase in withdrawal rate.

Retention of clay-solidified grouting curtain to Cd^(2+), Pb^(2+) and Hg^(2+) in landfill of municipal solid waste

The effects of components and their ratio of grouts on anti-seepage capability of clay-solidified grouting curtain and its permeability of heavy metal cations were investigated by permeating experiments, using reactive solute transport model to study the permeation of heavy metals (Cd2+, Pb2+ and Hg2+). The study of permeating for different mixture ratios of cement and clay indicates that hydraulic conductivity of clay-solidified grouting curtain with different ratios of solid to liquid or with the same ratio of solid to liquid but with different ratios of cement to clay is changed. The laboratory simulation test results also show that precipitates produced in heavy metal cation migration process in curtain block up water flowing passage which makes the hydraulic conductivity of the solution-permeated curtain decrease with the leakage time. The permeation velocities for different heavy metal cations vary with ionic concentration, exchange capacity and ion radius etc. The test results indicate that the permeation rapidity order of heavy metals cations in clay-solidified grouting curtain is Hg2+>Pb2+ in the same experimental circumstance. In addition, permeability for different mixture ratios and antisepsis capabilities of clay-solidified grouting curtain were studied in tests.

钢渣协同橡胶固化滨海港口淤泥的动力学特性研究

为研究钢渣协同橡胶固化滨海港口淤泥的动力学特性,对土样展开了动三轴强度试验,深入分析了钢渣掺量、橡胶颗粒掺量对滨海港口淤泥动力学特性的影响。研究表明:(1)各试样的滞回曲线形状相似,动应力-应变曲线变化趋势相同,动应力由近似线性迅速增长逐渐转变为近似水平缓慢增长并趋于稳定,说明试样由弹性变形逐渐转变为塑性变形;(2)钢渣掺入后,试样的动弹性模量获得显著提升,从抵抗变形角度来看,钢渣最佳掺量为65%;随着钢渣掺量的增加,试样的阻尼比逐渐降低,抗震性能逐渐减弱;(3)在65%钢渣改良淤泥土中继续掺加橡胶颗粒,会使试样的阻尼比增大,且阻尼比与橡胶颗粒掺量呈现正相关关系,橡胶颗粒掺量15%时阻尼比增加最为明显;但橡胶颗粒的加入会降低试样的动弹性模量,橡胶颗粒掺量10%时动弹性模量最大。

电网企业物资采购标准创新管理研究

本文在研究国家电网有限公司现有物资采购标准管理的基础上,介绍了电网企业物资采购标准模板管理和固化技术规范书管理两种标准创新应用管理方法,并从固化技术规范书动态管理和技术规范书分级分类两方面提出提升采购质效做法,为进一步提升物资管理水平,推动电网安全与高质量发展夯实基础。

社会阶层分化对当代青年发展的影响与应对策略

改革开放以来我国社会阶层分化呈现出了新的特征:流动性增强、不平衡性加剧、职业相关性显著、代际流动有强化趋势、社会底层的弱化与边缘化。高校大学生作为促进社会流动的重要群体也经受着困境与压力的双重掣肘,社会阶层分化对青年大学生也产生了一定的负面影响。本文在分析我国社会阶层分化及固化的现状与特征是影响青年思维、行为方式的重要因素,在制度、就业、思想引导等方面进行不断调整,建立缓释“社会阶层固化困局”的对策。

连铸工艺参数对轴承钢大方坏凝固行为的影响

连铸工艺参数对连铸产品质量有重要影响。文章建立了考虑铸坏表面实际水量分布的连铸凝固传热模型和CAFE模型,针对国内某钢厂生产的CCr15轴承钢展开模拟分析,探究了拉速、过热度、比水量对铸坏表面温度分布和凝固组织的影响规律。结果表明:拉速变化对整个连铸过程铸坏表面温度分布、二冷末端铸坏表面回温和铸坏液芯长度影响较大,当拉速由0.78m/min升高至0.98m/min时,二冷区末端铸坏表面回温值从102.9℃/m降低至91.6℃/m,铸坏液芯长度由18.8m增大到25.2m;过热度主要影响连铸坏CET开始转变位置和铸坏等轴晶率的大小,当过热度从10℃升高至40℃时,CET开始转变位置由距结晶器弯月面5.0m增大到16.7m,铸坏等轴晶率由42.7%降低至16.7%;比水量变化主要影响二冷区域连铸坏表面温度分布情况和二冷末端铸坏表面回温,当比水量从0.15L/Kg增大到0.40L/Kg时,二冷区末端铸坏表面回温值从78.2℃/m增加到129.8℃/m。为提高CCr15轴承钢连铸坏质量,在满足安全冶金准则要求的前提下,连铸坏拉速应控制在0.81m/min以上,二冷比水量应小于0.25L/Kg。当钢水过热度处于20-30℃范围内时,其变化对GCr15轴承钢铸坏等轴晶率和CET开始转变位置的影响最小。

快速凝固过共晶铝硅合金粉末特性

借助多级快冷装置（ＭＳＲＳ）配制了含磷分别为０．０４％，０．０８％和０．１２％（质量分数）的过共晶Ａｌ－２２Ｓｉ粉末，通过对粉末形貌、粒度、微观结构及点阵常数变化的研究，以图提高最终材料的塑性。结果表明，不同粒度的粉末组织存在差异，含磷０．０４％的Ａｌ－２２Ｓｉ合金粉末平均粒度最小，粉末中硅相得到了进一步细化，提高退火温度和延长保温时间导致硅相的粗化，４００℃×１ｈ或４８０℃×３０ｍｉｎ的退火条件下，硅相长大不明显。

Element segregation behavior of aluminum-copper alloy ZL205A

In aluminum-copper alloy, the segregation has a severe bad effect on the alloying degree, strength and corrosion resistance. A deeper understanding of element segregation behavior will have a great signif icance on the prevention of segregation. In the study, the element segregation behavior of ZL205 A aluminum-copper alloy was investigated by examining isothermally solidifi ed samples using scanning electron microscopy and energy dispersive spectroscopy. The calculated results of segregation coeffi cients show that Cu and Mn are negative segregation elements; while Ti, V and Zr are positive segregation elements. The sequence of element segregation degree from the greatest to the least in ZL205 A alloy is Cu, Mn, V, Ti, Zr and Al. The density of residual liquid is expected to increase with a decrease in the quenching temperature ranging from 630 ℃ to 550 ℃. The calculated results conf irm that the quenching temperature has an insignif icant effect on the liquid density; and the variation of density is mainly due to element segregation. Consequently, segregations of Al, Cu and Mn lead to an increase in density, but Ti, V and Zr present the opposite effect. The contribution of each element to the variation of the liquid density was analyzed. The sequence of contributions of alloying elements to the variation of total liquid density is Cu>Al>Mn>V>Ti>Zr.

Effect of SiC particle addition on microstructure of Mg_2Si/Al composite

In the present study, by adding SiC particles into Al-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced Al matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex situ stir casting. The as-cast microstructure containing primary Mg2Si and SiC particles that distribute homogenously in Al matrix was successfully achieved. The effects of SiC particle addition on the microstructure of Mg2Si/Al composites were investigated by using scanning electron microscopy(SEM) and XRD. The results show that, with increasing the fraction of the SiC particles from 5wt.% to 10wt.%, the morphologies of the primary Mg2Si particulates in the prepared samples remain polygonal, but the size of the primary phase decreases slightly. However, when the SiC particle addition reaches 15wt.%, the morphologies of the primary Mg2Si particulates change partially from polygonal to quadrangular with a decrease in size from 50 μm to 30 μm. The size of primary Al dendrites decreases with increasing fraction of the SiC particles from 0wt.% to 15wt.%. The morphology of the eutectic Mg2Si phase changes from a fi ber-form to a short fi ber-form and/or a dot-like shape with increasing fraction of the SiC particles. Furthermore, no signifi cant change in dendrite arm spacing(DAS) was observed in the presence of SiC particles.

热采井化学防砂剂试验研究

针对孤岛油田稠油油藏属疏松砂岩油藏易出砂这一现状研制开发了一种新型的热采井防砂剂，即ＲＣ—Ｇ防砂剂．这种防砂剂是在特制的ＴＬ颗粒表面涂敷一层带有潜伏性固化剂的高温粘合剂，注汽前挤入地层，在油层温度下，固化剂将粘合剂交联成不溶不熔体型产物，在油井近井地带形成一个较高强度的挡砂屏障，防止油井生产时出砂．这种防砂剂适用温度６０ ～３５０℃，３５０℃条件下抗折强度大于４．０ＭＰａ，渗透率可达３４．６μｍ ２，防砂不影响井的供液能力．采用这种防砂剂在热采井上试验１８ 井次，成功率８７．５％ ，和以往应用的高温涂敷砂相比，成功率明显提高，有一定的推广应用价值．

Simulation of stray grain formation at the platform during Ni-base single crystal superalloy DD403 casting

The mechanism of stray grain formation at the platform of turbine blade simulator and the effect of withdrawal rate(V) on the stray grain phenomenon have been investigated using a macro-scale Pro CAST coupled with a 3D Cellular Automaton Finite Element(CAFE) model. The results indicate that the stray grains nucleate at the edges of platform at V =150 μm·s^(-1) and 200 μm·s^(-1). Using Pro CAST computer simulation software, it was proven that the stray grain formation is signifi cantly dependent on the undercooling and the temperature fi eld distribution in the platform. The macroscopic curvature of the liquidus isotherm becomes markedly concave with an increase in the withdrawal rate. The probability of stray grain formation at the edges of platform can be increased by increasing the withdrawal rate in the range of 70 μm·s^(-1) to 200 μm·s^(-1).

Solidification of Mg-Zn-Zr Alloys:Grain Growth Restriction,Dendrite Coherency and Grain Size

The solidification characterization of Mg-xZn-0.5Zr(x=0,1,3,4,5 wt%)alloys has been extensively investigated through thermal analysis,microstructure characterization and thermodynamic calculations.The impact of Zn content on the grain growth restriction,dendrite coherency and thus the final grain size has been investigated and discussed.Increasing Zn content,the grain size of Mg-xZn-0.5Zr alloy was firstly refined and then coarsened with the finest grain size of^50μm for the Mg-3 Zn-0.5 Zr(ZK31)alloy.Significant effects of the grain size on the mechanical properties were observed in the investigated alloys.The combination of growth restriction factor theory and dendrite coherency point provides a reasonable explanation of the grain size results.It helps to further understand the mechanisms of grain refinement and grain coarsening related to solute content,providing reference for alloy design and grain size prediction.

变压器用植物绝缘油的低温特性试验研究

为研究凝点低的植物绝缘油对变压器绝缘强度的影响,用绝缘油耐压测试仪对凝固状态下的植物油、油纸绝缘结构进行耐压试验,并在高低温交变试验室对-30℃下的10 k V/315 k VA冷冻变压器实物进行耐压及局部放电试验。通过对比试验结果表明,对于大豆绝缘油,凝固后的绝缘油耐压下降了3.2 k V;油纸混合结构的耐压水平基本没变,凝固状态下的耐压值提高了1 k V;完全冷冻后的植物油变压器顺利通过耐压试验,且在最低气温为-27℃的内蒙古赤峰挂网运行23个月,运行情况良好。

粘土固化注浆帷幕对重金属离子的渗透实验分析

通过渗透实验研究了粘土固化注浆帷幕浆液配比对抗渗性能的影响,测试了其对重金属离子的抗渗性能,比较了不同重金属离子的迁移速度,并通过对比实验分析了其防腐性能。实验结果表明:粘土固化注浆帷幕的抗渗性能随着固相含量的增加而增强,且粘土对抗渗性能的贡献大于水泥;重金属离子在粘土固化注浆帷幕中迁移时可生成难溶的沉淀物,堵塞帷幕的导水通道,改善帷幕的孔隙结构和孔级配,使帷幕的抗渗性能随渗透历时逐渐增强;不同重金属离子在帷幕中的迁移速度不同,实验条件下的迁移速度Hg2+>Pb2+;实验验证了粘土固化注浆帷幕具有较好的防腐性能。

用新装置测定DP590钢的凝固相转变曲线

利用自行开发设计的高温凝固相转变测定装置,研究了DP590钢在不同冷速下的高温凝固相转变过程,得到了凝固过程中液相（L）到高温铁素体（δ）再到奥氏体（γ）的相变温度,并绘制了该钢的凝固相转变（SPT）曲线。结果表明：当冷速为0.006℃·s-1时,该钢δ相转变开始温度在1 520~1 535℃之间,结束温度在1 490℃左右;冷速增至0.33℃·s-1时,δ相转变开始温度降至1 510~1 520℃之间,结束温度在1 480~1 490℃之间;γ相转变开始温度为1 460℃之上,结束温度在1 435℃以下;随着冷速的增大,相转变模式会发生变化,相图会向下移动,各相变反应的温度区间减小。