Pore structure analysis of directionally solidified porous copper

Directionally solidified porous copper is considered as a potential candidate in the field of microchannel heat sinks.By the Bridgman-type directional solidification method,a porous copper ingot was fabricated.Evolution of the porosity,pore number density,average pore diameter and average interpore spacing at different ingot heights was investigated.The results show that with the increase of ingot height,the porosity firstly increases and then basically remains unchanged from the ignot height of 65 mm;the pore number density rapidly decreases at first,and the decreasing speed becomes slower when the ignot height higher than 85 mm;the average pore diameter increases and then remains unchanged from the ingot height of 85 mm;the average interpore spacing increases,and the increasing speed of average interpore spacing becomes slower with the increase of height to higher than 85 mm.In order to study the evolution of diameter and spatial distribution of pores,the distribution ranges of pore diameter,nearest-neighbor distance and radial cumulative pore number were analyzed.As the ingot height increases,the distribution ranges of pore diameter and nearest-neighbor distance firstly increase and then tend to be stable.There are no pore clusters and for long distance,the spatial distribution of pores is uniform at different ingot heights.Pore structure and 3D pore morphology of porous copper were observed with the help of light illumination and X-ray tomography.Pore nucleation,pore interruption,pore coalescence,diameter change of pores and lateral displacement of pores were found to exist in the pore structure.     

定向凝固藕状多孔Si的孔结构(英文)

采用定向凝固的方法,在一定的氢压条件下制备具有长孔结构的藕状多孔Si。通过调整凝固速率和氢气压力,铸锭的孔隙率、孔径和孔长度能够得到有效控制。实验结果表明:当其他条件不变时,铸锭的面孔隙率几乎不随凝固速率发生变化,但随着氢气压力的增加而逐渐降低。采用理论模型获得的不同氢压条件下制备出的铸锭体孔隙率预测结果与实验结果吻合较好。随着凝固速率和氢气压力的降低,铸锭的平均孔长度和孔径均逐渐增加,长径比则基本保持不变。通过将熔体的过热度从200 K提高到300 K,制备得到的试样其平均孔径增加约0.3mm,平均孔长度从7 mm提高至24 mm,平均长径比则由8提高至20。     

小直径长单晶铜线材的制备

在对单晶连铸技术长期研究的基础上，分析了制备小直径长单晶铜线材的几个关键技术问题，对传统的单晶连铸设备进行了改进。采用区域熔炼与热型连铸相结合的方法，为生产无限长、小直径单晶铜线材提供了可靠、稳定的设备与工艺．利用自制的铜线材单晶化设备，对生产长单晶铜线材的工艺进行了研究。结果表明：形成向液态金属中凸出的液固界面是制备单晶线材的基础，液固界面所处的位置是保证单晶线材质量稳定的关键。在加热铸型内部距型口5mm左右的位置保持液固界面呈向液态金属中凸出的形状．可以保证获得质量稳定的单晶铜线材。     

藕状多孔铜的连铸法制备工艺研究

连铸法是一种制备具有均匀孔洞分布的大尺寸藕状多孔材料的新工艺.利用自行开发的GASAR连铸装置,成功拉制出了15 mm的藕状多孔Cu连铸试样,并研究了下拉速率对孔隙率及气孔直径的影响.结果表明:随着下拉速率的增加,连铸试样中气孔尺寸分布逐渐变均匀;下拉速率对孔隙率的影响不大,而气孔直径随下拉速率的增加而降低.     

Nb-Mo-Si共晶合金的定向凝固组织特征

采用光悬浮区熔定向凝固技术制备了Nb-Mo-Si三元共晶合金,研究了试棒旋转速度和抽拉速度对Nbss-β(Nb,Mo)5Si3共晶组织形态的影响。结果表明籽晶棒的旋转对组织形态有显著影响,而料棒的旋转对组织形态的影响并不明显。当抽拉速度是5mm/h,籽晶棒不旋转时,得到了规则的Nbss-β(Nb,Mo)5Si3片层结构;而当籽晶棒旋转时,试棒中心处为先析出的球状Nbss和规则片层组织,沿径向向外,规则的片层组织逐步转变成不规则的碎块状组织。当籽晶棒不旋转,抽拉速度是1mm/h时,组织为不规则共晶组织,Nbss倾向于连成网状;当抽拉速度是3～5mm/h时,形成典型的规则片层组织;当抽拉速度是10mm/h时,具有片层组织的柱状晶和胞状晶共存。此外,从液/固界面特性及过冷度的角度对组织多样性进行了讨论。     

Effect of transference velocity and hydrogen pressure on porosity and pore morphology of lotus-type porous copper fabricated by a continuous casting technique

A continuous casting technique was developed to fabricate, in a pressurized hydrogen atmosphere, lotus-type porous copper with long cylindrical pores aligned parallel to the solidification direction. The molten copper dissolving the hydrogen was pulled downward to be solidified through a cooled mould at a given transference velocity. This technique has the benefit of producing long-sized lotus-type porous metal slabs as long as 700 mm. The effects of the hydrogen gas pressure and the transference velocity on the porosity and the pore morphology were investigated. The porosity was independent of the transference velocity but dependent on the hydrogen gas pressure. The average pore diameter and pore length were affected by the changes of both the transference velocity and hydrogen gas pressure. The change of transference velocity affected the pore formation position near the slab surface. The porosity and pore size were therefore well controlled by the transference velocity and hydrogen gas pressure. It is concluded that the continuous casting technique is a promising method for the mass production of lotus-type porous metals.     

Zn-5%Al合金定向凝固液固界面形态分析

对Zn-5%Al合金在不同液淬下拉速率和过热状态下的定向凝固液固界面形态进行了研究。结果表明,当合金熔体的过热温度分别为较低和较高时,随着液淬下拉速率的增加,定向凝固界面形态变化与一般的界面形态演化相比各自表现为相符和相异;定向凝固界面稳定性变化存在着若干个由液淬下拉速率和过热状态互相制约决定的分界点。     

去合金化工艺对纳米多孔铜孔结构的影响

以Mn-Cu合金为前驱体合金,在酸溶液中腐蚀去合金化成功制备出孔径尺寸为纳米量级的纳米多孔铜。 研究了去合金化工艺参数中的酸溶液成分、腐蚀时间及腐蚀温度对最终纳米多孔铜孔结构及Mn的选择性腐蚀程度影响。结果表明：在0.1 mol/L HCl溶液中自由腐蚀去合金化后可得到孔结构均匀的纳米多孔铜;随着腐蚀时间的延长,孔结构有显著变化,腐蚀2 d所得纳米多孔铜样品的孔结构呈蜂窝状,腐蚀5 d所得样品的孔结构呈均匀的三维网络状结构,而后随着腐蚀时间的延长,孔壁逐渐粗化;随着腐蚀温度升高到60 ℃,样品中的残余Mn含量降低明显。通过调整去合金化工艺,实验所制备的纳米多孔铜孔结构呈均匀的三维网络状,孔隙率为57.7%,平均孔径尺寸约140 nm。     

B30铜合金电渣重熔工艺实践

采用熔点比铜合金熔点低100～200℃的MgF2-CaF2渣系重熔B30铜合金,熔化速率(kg/h)控制在(1～1.3)×结晶器直径(mm),有利于改善电渣锭的表面质量,提高铜合金纯净度和电渣锭致密度,改善锻造性能。     

多孔Cu/Ni复合材料的电沉积法制备及其性能研究

采用电沉积方法制备了孔隙分布均匀且沉积层从 2到 5 层的多孔Cu/Ni复合材料。研究了不同工艺参数对多孔Cu/Ni复合材料的微观结构形貌和力学性能。多孔Cu/Ni复合材料的微观结构形貌与表征参数与沉积层数密切相关,其平均孔径、孔隙率随沉积层数增加而减小,其比表面积、表观密度随沉积层数增加而增大,多孔Cu/Ni复合材料的铜层与镍层之间由于原子扩散形成固溶体合金层。材料的力学性能随沉积层数增加而提高,压缩强度可达 17.36 MPa,杨氏模量增加 7.9倍,单位体积吸能本领提高13.9倍。     

润湿性及孔径均匀性对铜液在多孔W骨架中渗流过程的影响

采用Voronoi随机算法建立微尺度W骨架多孔模型,基于Young-Laplace修正后的Navier-Stokes动量方程,应用有限体积法分析制备CuW合金的渗流过程。模拟结果表明:Cu-W间的润湿性越好,则铜液流股中心流速越大,但铜液在骨架壁面的黏附越强,从而有利于铜液与壁面接触而产生机械结合。此外,渗流通道中由于孔径不均匀引起的扩孔与缩孔转变导致铜液在孔隙中形成漩涡,促使CuW合金中产生气孔,从而降低铜液的充填率。     

多孔储液材料的仿生制备及其摩擦学性能研究进展∗

多孔储液材料因其优异的自润滑性能备受关注,特别是其孔隙结构参数与性能间对应关系的研究一直是学术界和工业界亟待解决的问题。 针对该类多孔储液材料,从来源、制备方法以及摩擦学特性等方面对其发展脉络及面临的问题进行梳理和分析,认为在仿生关节软骨制备适合工业应用的摩擦副方面,如何提取关键仿生特征参数是关键。 目前在进行服役可靠性、工况适应性分析时,多用孔隙率来表征多孔结构特征,在明晰孔隙形态参数(孔径,分布,贯通型等)与力学-物理性能、润滑状态之间的映射关系方面存在明显的不足,导致从优化孔隙形态参数入手实现多孔储液材料力学-物理性能与摩擦学性能的统一方面仍具挑战性。 3D 打印技术的快速发展有望解决当前多孔材料成形过程中孔隙形态参数不可精确控制的问题,并为其自润滑理论的发展提供有效试验手段。     

工艺参数对藕状多孔Mg合金结构影响的模拟仿真

在金属/气体共晶定向凝固工艺(Gasar)中,气体压力、过热度以及凝固速率是影响藕状多孔金属结构的最重要参数。建立了一个描述Gasar工艺过程的传热、传质、气孔形核、生长、合并及气孔与固相的协同生长的三维非稳态理论模型。并且采用有限差分的方式,实现了定向凝固铸造法Gasar工艺过程中藕状多孔结构形成及演变的计算机仿真,揭示了气体压力和凝固速率对藕状多孔金属最终结构参数的影响。基于Mg-H系的模拟与相应试验结果吻合较好,验证了所建仿真模型的合理性。     

粉末特性对多孔不锈钢制备工艺和结构的影响

以凝胶注模工艺为基础,结合微波烧结技术,制备了形状和孔隙可控的多孔不锈钢材料。采用扫描电子显微镜、密度仪、抗弯实验等手段研究了粉末粒径、粉末形状、固相含量等特性对多孔不锈钢制备工艺和孔隙形貌、孔隙率的影响。结果表明:粉末粒径越小,形状因子越大,胶体固相含量越高,制备得到的多孔不锈钢的孔隙率越高;粉末形状因子越小,多孔不锈钢的孔隙越不均匀;固相含量越高,虽然坯体强度有所提高,但凝胶体系的粘度也越大,流动性较差,适合不锈钢粉末凝胶注模的最佳固相含量在58%左右。通过控制颗粒直径、颗粒形状、固相含量及采用颗粒级配的方法,可实现对凝胶注模制备多孔不锈钢的孔隙结构和孔隙率的有效控制。     

多孔金属结合剂CBN砂轮孔隙结构对磨料层胎体力学性能的影响

为解决多孔金属结合剂CBN砂轮在高孔隙率下的强度下降问题,采用球形尿素颗粒为造孔剂,制作孔径、孔形和孔隙可控的多孔金属结合剂砂轮磨料层胎体,研究不同载荷情况下的孔隙率和孔隙排布等孔隙结构因素,对多孔金属结合剂磨料层胎体力学性能的影响规律。结果表明:孔隙有序排布时的胎体弹性模量要小于孔隙无序排布的;胎体材料的屈服强度随孔隙率增大而下降;在相同孔隙率下,孔隙有序排布的胎体,在纵向受压、孔隙正向排布的情况下屈服强度更高。      

熔体过热历史对Ni基高温合金定向凝固界面形态的影响

在控制温度梯度、抽拉速率等工艺参数相同的条件下,首次发现熔体过热历史对Ni基高温合金定向凝固界面形态具有显著影响．随着熔体过热温度的提高和过热时间的延长,液固界面稳定性降低;相反,随着低温静置时间的延长,液固界面稳定性提高．熔体热历史对定向凝固液固界面形态影响的根本原因在于对熔体结构状态的改变,进而影响凝固过程.     

Effect of Dy on the microstructures of directionally solidified NiAl–Cr(Mo) hypereutectic alloy at different withdrawal rates

The effect of various Dy content on the microstructure of Ni–31Al–32Cr–6Mo hypereutectic alloy was studied at the withdrawal rates of 6, 30 and 90 μm/s. The results show that the solid–liquid interface morphology has an evolutionary process of planar → cellular → dendritic interface with the increasing withdrawal rate. The primary Cr(Mo) dendrites are gradually weeded out through competitive growth between the primary phase and the eutectic phase. The volume fraction of primary Cr(Mo) dendrites decreases with the modest addition of Dy (0.05 wt.%) at 6 μm/s. When the withdrawal rate increases to 30 μm/s, the appropriate addition of Dy (0.1 wt.%) refines the microstructure, such as the width of intercellular zone and the lamellar thickness in the intercellular zone. With the increase of withdrawal rate to 90 μm/s, the addition of Dy has no significant effect on the microstructure. In addition, the white Dy-containing phase can occur in the boundary of eutectic cells when the Dy content is no less than 0.1 wt.%.     

Study on Micron Porous Copper Prepared by Physical Vacuum Dealloying

Porous copper was prepared successfully by physical vacuum dealloying method using the Cu Zn alloy precursors(Cu30Zn70, Cu40Zn60 and Cu50Zn50 alloys). The micron porous copper showed a three-dimensional continuous porous structure with 1–5 μm pore size. With the increase of the Zn content in the CuZn alloy, the pore structure of the porous copper was more uniform and ordered. Temperature was the key factor for physical dealloying, and the optimized temperature was 500 °C for the CuZn alloy. The pores would fuse and disappear when the temperature was over 500 °C.Physical vacuum dealloying was an effective preparation method for porous copper, which can be used to prepare other porous metals based on the sublimation and the Kirkendall effect.     

FRACTAL ANALYSES OF DIRECTIONAL SOLIDIFICATION BEHAVIOR OF A Ni-BASE SUPERALLOY

The morphology of solid/liquid interface of a directionally solidification process is describedby means of fractal analysis,and the relations among the fractal dimension of the solid/liq-uid interface,solidification rate,dendrite arm space and the phosphorus content of the test al-loys have been given.It was found that the increase of the solidification rate and the phos-phorus content of the test alloy will lead to a increase,following the regularity of exponentialfunction,in the fractal dimension of solid/liquid interface.Furthermore,by combining thefractal theory and the thermodynamic principle with the measured results,it has been provedthat the fractal dimension is not only a kind of simple geometrical parameter used in des-cribing irregular geometry,but also a state function depending the change of solidificationparameters and chemical compositions.     

Effect of withdrawal velocity on dendritic interfacial characteristic for Al-Cu alloy during directional solidification

采用Al-4%Cu合金, 对不同抽拉速率下定向凝固枝晶界面特征进行了研究. 结果表明, 当抽拉速率从100 um/s增至600 um/s时, 一次枝晶间距随抽拉速率的增大而减小. 在枝晶固/液 界面存在枝晶干的凸起, 其平--凸--平--凸的程度随抽拉速率的增加呈现先加强后减弱最后几乎消 失的规律. 随着抽拉速率的增大, 枝晶尖端温度先升高而后降低. 采用KGT模型和非平衡效应 研究了枝晶界面温度, 分析了尖端过冷度和尖端成分对枝晶界面特征的影响, 得到非平衡凝固枝 晶尖端过冷度的计算方程. 界面平-凸-平-凸的程度与枝晶尖端成分和尖端过冷度有关.