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。     

Structure and oil retaining capacity of gasar copper fabricated by radial solidification with a combined crystallizer

Porous copper with elongated pores was fabricated by a radial solidification method. The process was carried out in a combined crystallizer under high pressure of a mixture of hydrogen and argon. Pore size, pore length, pore density and porosity of the porous copper were characterized. Furthermore, the oil retaining capacity including oil content and oil efficiency was also evaluated. It is found that porous copper solidified with water-circulated chiller through a thick graphite jacket possesses a gradient structure with increasing pore size, and thus pore density decreases. Also pore length and pore aspect ratio decrease from lateral inwardly, while its porosity is almost uniform. The results show that the porous copper with radial pores has a good oil retaining capacity.     

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.     

Gasar工艺下藕状多孔银的气孔结构研究

金属-气体共晶定向凝固（Gasar)是制备藕状多孔金属的新工艺,利用自行研制的Gasar装置,成功地制备了不同纯氧分压下的藕状多孔银试样,研究了氧气分压对藕状多孔银气孔形貌（气孔率、气孔尺寸和分布、气泡形核）的影响。结果表明：氧气分压对气孔形貌影响十分显著。随着氧气压力的增加,气孔率增大而平均气孔直径减小。     

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.     

Oil retaining capability and sliding friction behaviour of porous copper with elongated cylindrical pores

Porous copper with elongated cylindrical pores aligned either axially or radially was fabricated under a high pressure of mixture gas of hydrogen and argon. Structure characterization indicated that pore size increased, pore density decreased, pore size distribution became wider with an increase in porosity for the porous copper. The dependence of oil retaining capability and sliding friction coefficient on porosity and pore size of the porous copper were investigated. It was found that the oil content of the porous copper depended mainly on the porosity, and reached 27.6% on the specimen with a porosity of 47.1%. On the other hand, the oil efficiency was not satisfactory, and became worse when the porosity increased, which was attributed to the increase in pore size and the wider pore size distribution for the porous copper. It was proven that the impregnated oil in the pores played an important role in improving the sliding friction behaviour of the porous copper.     

定向凝固多孔Cu热沉传热性能的实验研究

利用定向凝固多孔Cu制备了气孔呈定向规则排布的多孔Cu热沉,对沿孔长方向长度20 mm热沉的传热性能进行了实验研究.实验结果表明,定向凝固多孔Cu热沉具有优异的传热性能,当气孔率为29%,平均孔径为400μm时,热沉的换热系数可以达到5 W/(cm~2·K),沿孔长垂直方向将定向凝固多孔Cu切割成沿孔长方向排列的2段后,其换热系数可以提高到6.5 W/(cm~2·K).这说明当定向凝固多孔Cu沿孔长方向的长度较大时,通孔率降低限制了热沉的传热性能.     

Synthesis of anodic aluminum oxide (AAO) at relatively high temperatures. Study of the influence of anodization conditions on the alumina structural features

Anodic aluminum oxide (AAO) is a well known template for nanofabrication. Structural features of AAO like pore diameter, interpore distance, porosity, pore density can be fully controlled by operating conditions of anodization. Typically, self-organized two-step anodization is carried out at low temperature (below room temperature) and is a time consuming process. There are individual experiments describing anodization at temperatures close to room temperature. In our study, furthermore, a systematic analysis of the anodization condition influence on the nanoporous alumina structural features was done. The anodization temperature was ranging from 35 to 50 °C increasing significantly current density of the processes, which has increased oxide film growth rate. The anodizing potential ranged from 20 to 60 V and time of the anodization steps was 30, 60 or 120 min. The data obtained has shown that the pore diameter increases with potential, temperature and time of anodization, while the interpore distance is influenced solely by the potential. Temperature and time changes do not affect the interpore distance. Porosity is also influenced by potential, temperature and duration of anodization. Pore density is influenced only by the potential. The synthesis of AAO reported here gives possibilities to obtain the AAO templates in a faster and cheaper way, essential for researchers applying anodic alumina as a template.     

气压对定向凝固藕状多孔镁的气孔分布影响

采用统计分析方法,通过孔径分布、气孔最邻近距离和局部气孔率定量分析定向凝固藕状多孔镁横截面上的气孔分布特征,并在此基础上分析气压对藕状多孔镁气孔分布的作用规律。结果表明:纯氢条件下气压越高,孔尺寸分布越趋于一致、孔位置和气孔结构单元分布越均匀;氢气分压一定,选择合适的氩气分压可使熔体共晶凝固时,孔尺寸、孔位置和气孔结构单元的分布最均匀。     

Influence of Al-B grain refiner on porosity formation of directionally solidified Al-Si alloys

This work aims to present a perspective for porosity formation in three different alloys:A356,A413 and A380.1 by taking into account the addition of Al-B grain refiners:AlTi_5B_1 and Al_3B.The directional solidification method was used,and microstructural changes of the alloys and its correlation with porosity formation were investigated.Pore size,number of pores,average pore length and distribution of pores were statistically analyzed.Also,external shrinkage was examined,and the volume of external shrinkage was calculated.It was found that there was a relationship between external shrinkage and the size and number of pores.As the size and number of pores internally decrease,external shrinkage increases.Additionally,porosity is decreased in all the three Al-Si alloys when Al-B grain refiners are used.The distribution of pore diameters is low when AlTi_5B_1 is used.Grain refiners have a different effect on porosity formation of Al-Si alloys with regard to their solidification morphology.     

The effect of n-alcohols on porous anodic alumina formed by self-organized two-step anodizing of aluminum in phosphoric acid

Self-ordered porous anodic alumina films were fabricated by a two-step anodization technique at potentials between 110 and 170 V using different n-alcohols and water mixtures containing 0.3 M H₃PO₄ at the electrolyte temperatures of 0 and − 5 °C. The morphology of the specimens was observed by a field emission scanning electron microscope (FE-SEM). Anodic aluminum oxide (AAO) films fabricated in the absence of n-alcohols exhibit a complex structure with sub-pores, independently of the anodizing potential. The sub-pore structure of films disappeared in the presence of n-alcohols probably due to the cooling effect of alcohol and extended time for the pore interaction (re-arrangement of pores). Additionally, with increasing anodizing potential, the regularity of pore arrangement, uniformity of pore shape and interpore distance of the AAO film increases independently of the electrolyte composition. The order of arrangement and circular shape of pores increases with increasing n-alcohol content for both anodizing temperatures. The best arranged porous structures were obtained in 1:1 methanol-water electrolyte containing 0.3 M H₃PO₄ (lower evaporating point than n-propanol and water) at 0 °C. The interpore distance of porous anodic alumina decreases with increasing n-alcohol content and increasing regularity of pore arrangement.     

Influence of Structural Parameters on Tensile Property of Gasar Porous Copper

采用金属-气体共晶定向凝固工艺,制备了不同结构参数的Gasar多孔铜,并研究了结构参数对单向拉伸下多孔铜性能的影响。利用扫描电镜观察拉伸试样的断面形貌,通过建立数学模型和计算机模拟的方法来表征其拉伸强度,并用实验数据加以验证。结果表明,多孔铜的拉伸性能主要取决于气孔率和拉伸方向;多孔铜在平行气孔轴向拉伸时比垂直气孔轴向拉伸时具有更优异的抗拉强度;平行气孔轴向拉伸时,抗拉强度随着气孔率的增加线性下降,气孔对基体的应力集中作用微小,抗拉强度的数学模型数值和模拟数值与试验数值拟合良好;垂直气孔轴向拉伸时,抗拉强度随气孔率的增大而明显下降,气孔对基体的应力集中作用显著,抗拉强度的试验数值与模型数值以及模拟数值基本符合     

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 field simulation was carried out based on ProCast software to investigate the shape and movement velocity of the solidifying solid/liquid interface. The experimental results show that the solidification 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.     

定向凝固多孔Mg-Zn合金的制备及气孔结构

采用Bridgman型定向凝固法制备出藕状多孔Mg-Zn合金.研究了不同锌含量和氢气压力对气孔形貌的影响.通过理论计算对Mg-1Zn(质量分数,％,下同)合金的孔隙率进行了预测.结果表明,锌元素的加入会对孔结构产生重大影响.随着Zn含量从0％增加到2％,平均孔径增加.随着氢气压力从0.1 MPa增加到0.6 MPa,M...     

规则多孔金属理想结构分析

在氢气或氢气和氩气混合的高压气氛中,采用定向凝固技术制得了规则多孔Cu。对不同直径和不同气孔率的试样进行了图像处理;计算了各可能结构的理论气孔率,并与实测值比较;计算了各结构生成吉布斯能;对比了各结构的演化完整性。结果表明,正六边形气孔率理论计算值与实测值偏差最小;正六边形结构生成吉布斯能最低;正六边形结构无空位和中断,具有完好的演化性。正六边形是规则多孔金属气孔析出的理想结构。     

热喷涂热障涂层孔隙与涂层性能关系研究进展

孔隙在热障涂层中较为常见,孔隙对热障涂层的性能有利有弊。对热障涂层陶瓷层中孔隙的形成机理进行了综合分析,总结了热障涂层孔隙结构的调控方法,讨论了孔隙结构特征对热障涂层隔热性能和力学性能的影响。孔隙结构的引入将引起力学性能的下降,同时降低热障涂层的热导率,提高隔热效果。孔隙结构特征参数包括孔隙形状、孔隙间距、孔隙倾斜角、孔隙高宽比等,其中孔隙的倾斜角和高宽比对涂层导热性能的影响尤为重要,是孔隙结构的关键特征参数。通过原始粉末孔隙结构的保留、造孔剂(有机造孔剂、无机造孔剂)的搭配造孔、制备工艺(临界等离子喷涂参数、粒子扁平率等)的调节以及后续的孔隙处理,可实现热障涂层孔隙结构的调控。在实际应用过程中应同时兼顾力学性能和隔热性能,最重要的是保证热障涂层的有效寿命,需要综合考虑力学性能与导热性能的匹配。通过热障涂层孔隙结构特征的设计及分布控制,可实现孔隙结构高性能、高可靠性热障涂层的制备。     

Fabrication of lotus-type porous Mg−Mn alloys by metal/gas eutectic unidirectional solidification

Lotus-type porous Mg–xMn (x=0, 1, 2 and 3 wt.%) alloys were fabricated by metal/gas eutectic unidirectional solidification (the Gasar process). The effects of Mn addition and the fabrication process on the porosity, pore diameter and microstructure of the porous Mg−Mn alloy were investigated. Mn addition improved the Mn precipitates and increased the porosity and pore diameter. With increasing hydrogen pressure from 0.1 to 0.6 MPa, the overall porosity of the Mg−2wt.%Mn ingot decreased from 55.3% to 38.4%, and the average pore diameter also decreased from 2465 to 312 μm. Based on a theoretical model of the change in the porosity with the hydrogen pressure, the calculated results were in good agreement with the experimental results. It is shown that this technique is a promising method to fabricate Gasar Mg–Mn alloys with uniform and controllable pore structure.     

藕状多孔铜沿垂直于气孔方向的压缩变形行为与本构关系

采用定向凝固法,在氢气压力为0.2 MPa,熔体温度为1 200 ℃的条件下制备d 45 mm×120 mm的藕状多孔纯铜棒材,研究藕状多孔金属垂直于气孔方向的压缩变形过程及其影响因素,分析压缩变形机理.结果表明:藕状多孔铜沿垂直于气孔方向的压缩变形过程可分为弹性变形、气孔的塑性屈曲、气孔的密实化和密实化后的塑性变形4个阶段,其中塑性屈曲阶段的主要变形机理为多孔材料在垂直载荷的作用下先后形成若干个变形带,在变形带内圆形气孔先后以压扁和塌陷的方式进行塑性变形;采用回归分析方法建立藕状多孔金属沿垂直于气孔方向的压缩变形本构关系.     

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。      

Effects of cell size on compression and bending strength of aluminum-foamed material by complex stirring in induction heating

This paper investigated the effects of various process parameters on the mechanical properties of aluminum-foamed material. For the sake of this, complex stirring, which combined electromagnetic stirring with mechanical stirring, was used to fabricate aluminum foam materials by varying fabrication conditions. Pore size and its volume fraction increased as temperature of molten metal increased. When stirring, pore generation increased and distribution state improved as the stirring velocity increased. Pore size and porosity fraction increased as the foaming velocity increased. It resulted in pore size and shape to be poor material properties. Pore size and porosity fraction increased as the foaming temperature increased. However, the inner flow by the expansion in the molten metal due to temperature gradient and gravitational liquid metal drainage into inter-pores would occur, which caused pores deformed. The compressive strength was inversely proportional to the cell sizes. The yield strength below 2 mm of cell size changed gradually, but the yield strength over 2 mm of cell size drastically decreased because the shape of cell changed from spheroidal to polyhedral structure.