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。     

纯氧分压Gasar工艺下藕状多孔银的气孔结构研究（英文）

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,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。     

Ag-O系定向凝固制备藕状多孔Ag

金属-气体共晶定向凝固(Gasar)是一种制备藕状多孔金属的新工艺,在高压纯氧气氛中,利用自行研制的Gasar模铸装置制备了藕状多孔Ag试样,并研究了氧气压力对气孔率、平均气孔直径的影响。结果表明:在多孔Ag中,氧气压力对气孔率和平均气孔直径的影响十分显著。随着氧气压力的增加,气孔率增大,而平均气孔直径减少,当氧气压力为0.5 MPa时,气孔分布最为均匀。     

多孔Cu的气孔特性及其热力学数学模型

以氢共晶合金为对象,通过建立热力学数学模型,研究定向凝固工艺对氢共晶合金中气孔平均间距与直径的影响。结果表明,多孔Cu连铸试样中气孔的平均间距和直径随着下拉速率的增加而逐渐减小。下拉速率较小时,理论预测与实际测量结果存在明显差异。随着下拉速率的增加,两者的吻合度提高,预测效果较好。     

区域熔炼法制备藕状多孔铜

采用区域熔炼法在氢气氛下制备了藕状多孔铜,其气孔呈圆柱状沿凝固方向分布。研究了凝固速率对气孔率、气孔直径和气孔数密度的影响。结果表明:气孔率随凝固速率的增加而增大;凝固速率的增加能促进气泡形核,使平均气孔直径减小而气孔数密度增大。所制备的藕状多孔铜的气孔率和气孔直径可通过调节凝固速率而得到控制。     

藕状多孔纯Cu及多孔Cu-1.8%Cr合金铸件的研究

利用自行开发的GASAR装置,成功制备出藕状多孔纯Cu及多孔Cu-1.8%Cr合金试样,并对其孔隙率、平均气孔直径、基体组织及压缩特性进行了相应的对比研究。结果表明:随着凝固高度的增加,气孔率保持不变,而平均气孔直径增大,且多孔Cu-1.8%Cr合金的气孔率和平均气孔直径高于多孔纯Cu;藕状多孔纯Cu的定向凝固组织是由粗大的Cu晶粒组成,而多孔Cu-1.8%Cr合金的定向凝固组织为白色细小的α固溶体、灰色的共晶相(α+β)以及少量颗粒状的单相Cr质点组成;藕状多孔纯Cu及多孔Cu-1.8%Cr合金的压缩应力-应变曲线均由弹性变形阶段、屈服平台阶段及密实化阶段组成,但是Cr的加入使得藕状多孔纯Cu的压缩性能得到较大提高——杨氏模量和屈服强度增加而加工硬化指数降低。     

藕状多孔纯铜棒的制备与表征

采用定向凝固法,在氢气压力为0.2 MPa、熔炼温度为1 200℃的条件下制备了规则圆柱形气孔沿轴向定向分布的藕状多孔纯铜棒材料,棒材直径为45 mm,长度约为125 mm.测定了所制备材料的密度、孔隙率和通孔率,对所制备多孔材料的气孔形貌和气孔大小分布进行了分析和表征,并对所制备的样品沿平行于气孔方向和垂直于气孔方向的压缩性能进行了测试.结果表明,所制备纯铜棒的平均密度为4.48 g/cm3,平均孔隙率为50%;气孔直径分布为0.3～1.3 mm,气孔平均直径为0.81 mm;藕状多孔纯铜的压缩性能存在明显的各向异性.     

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。     

应变速率对藕状多孔镁垂直于气孔方向压缩变形行为与力学性能的影响EI北大核心CSCD

利用定向凝固法制备藕状多孔镁,采用GLEEBLE^(-1)500型材料模拟实验机和分离式霍普金森压杆(SHPB)装置,在以1×10^(-3)~1650 s^(-1)的应变速率范围内沿垂直于气孔方向进行压缩实验,研究应变速率对藕状多孔镁压缩变形行为和力学性能的影响。结果表明:当垂直于气孔方向压缩时,藕状多孔镁的应力-应变曲线分为应力线性增加的弹性阶段、应力缓慢增加的平台阶段和应力急剧增加的密实化阶段,应力随应变的增加持续增大,无应力峰值的出现。而当垂直于气孔方向压缩时,应变速率对藕状多孔镁的变形行为影响显著,在应变速率ε<60 s^(-1)条件下,主要变形方式为气孔先发生椭圆化变形,然后部分气孔的孔壁率先向气孔内发生弯月形塌陷并形成垂直于压缩方向的先变形带,随后变形带不断产生,从而逐步实现密实化;而较高应变速率(ε=450~1650 s^(-1))下的变形方式虽然气孔也是先后发生椭圆化、孔壁向气孔内的弯曲塌陷等变形并形成先变形带,但先变形带沿试样对角线方向率先形成,并随压缩进行不断向与对角线垂直的方向扩展。应变速率对藕状多孔镁的力学性能有较明显的影响,其影响机制主要是由于不同应变速率时气孔的变形方式发生了变化。     

应变速率对藕状多孔镁垂直于气孔方向压缩变形行为与力学性能的影响

利用定向凝固法制备藕状多孔镁,采用GLEEBLE~(-1)500型材料模拟实验机和分离式霍普金森压杆(SHPB)装置,在以1×10~(-3)~1650 s~(-1)的应变速率范围内沿垂直于气孔方向进行压缩实验,研究应变速率对藕状多孔镁压缩变形行为和力学性能的影响。结果表明:当垂直于气孔方向压缩时,藕状多孔镁的应力-应变曲线分为应力线性增加的弹性阶段、应力缓慢增加的平台阶段和应力急剧增加的密实化阶段,应力随应变的增加持续增大,无应力峰值的出现。而当垂直于气孔方向压缩时,应变速率对藕状多孔镁的变形行为影响显著,在应变速率ε60 s~(-1)条件下,主要变形方式为气孔先发生椭圆化变形,然后部分气孔的孔壁率先向气孔内发生弯月形塌陷并形成垂直于压缩方向的先变形带,随后变形带不断产生,从而逐步实现密实化;而较高应变速率(ε=450~1650 s~(-1))下的变形方式虽然气孔也是先后发生椭圆化、孔壁向气孔内的弯曲塌陷等变形并形成先变形带,但先变形带沿试样对角线方向率先形成,并随压缩进行不断向与对角线垂直的方向扩展。应变速率对藕状多孔镁的力学性能有较明显的影响,其影响机制主要是由于不同应变速率时气孔的变形方式发生了变化。     

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.     

连铸法Gasar工艺中抽拉速率对多孔金属结构影响的理论分析

通过求解凝固界面前沿熔体中的溶质浓度场方程,从理论上建立了一个用于描述连铸法Gasar工艺中的工艺参数对藕状多孔金属结构平均孔径、孔间距以及气孔率影响的理论模型,并将抽拉速率对多孔金属结构的影响的理论预测结果与文献中相应实验结果进行比较,结果表明,理论预测结果与实验结果吻合较好.预测结果显示,平均孔径r_g和孔间距L随抽拉速率v的升高不断降低,但气孔率变化较小,它们之间存在着简单关系为:r_g~(1.72)·v=A和L~(1.72)·v=B(其中,A和B都是取决于气体压力pH_2和pA_r以及熔体温度T的常数)。     

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。     

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.     

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.     

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.     

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.     

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。     

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.