Gasar工艺获得均匀藕状多孔结构的气压选择

在用金属-气体共晶定向凝固（Gasar）制备藕状规则多孔金属的工艺中,气体压力是对多孔结构影响最大且最方便调控的工艺参数,在讨论Gasar工艺中所用气体种类选择原则的基础上,通过分析Gasar凝固过程,给出了获得指定气孔率且气孔尺寸分布和位置分布都均匀一致的理想藕状多孔结构的气压选择条件．以Mg-H系为例从实验上验证了该选择条件,为制备高质量的藕状多孔金属提供了合理的工艺参数．     

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。     

GASAR多孔Cu-1.3Cr合金制备及结构特征

采用金属/H2共晶定向凝固技术在纯H2气氛下制备了不同气压条件下的多孔Cu-1.3Cr合金,研究了气体压力对多孔Cu-1.3Cr合金气孔结构和分布的影响。结果表明,在纯H2条件下,平均孔隙率随气压升高逐渐增大,当气压超过0.5 MPa时,由于气体逸出造成孔隙率有所下降;气孔平均孔径随气压升高而减小;气压越高,气孔越多,气孔分布越均匀。同时,气孔的尺寸分布范围变窄,气孔间距变小。     

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.     

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。     

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。     

藕状规则多孔结构形成的压力条件和气孔尺寸的演变规律

金属-气体共晶定向凝固（Gasar）是一种制备规则多孔金属的新工艺,本工作通过分析气泡的生长条件,建立了藕状多孔结构形成的压力判据（H2气和Ar气分压比）,并从实验上研究了凝固压力对气孔尺寸的影响规律,结果表明,随着凝固压力（气体总压）的增大,气孔平均直径不断降低。     

基于纳米CT技术的藕状多孔铜三维重构的研究

利用定向凝固法分别在0.55、0.7及1mm/s的拉速下制备出了具有规则气孔分布的藕状多孔铜,并采用非破坏性纳米CT扫描技术对所制备的多孔铜结构进行CT扫描及三维体重构,研究了拉速对气孔形核及形核数目、气孔率以及孔径大小和分布的影响。结果表明,随着凝固进行,气孔形核数目逐渐减少并且趋于稳定,在整个定向凝固过程中,都存在新气孔的形核现象。当拉速增加时,铸锭在相同高度范围内新气孔的形核数目增加,气孔的平均直径减小,气孔的尺寸分布均匀性下降。     

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。     

小管路焊缝内部缺陷的三维X射线成像

基于X射线显微CT技术,对小直径管路焊缝试样内部缺陷和内表面质量进行了三维观察,发现了5个近球形气孔缺陷. 通过三维可视化显示了气孔缺陷的空间位置分布,并量化分析了气孔缺陷的位置、体积、直径、球度等三维特征参数,量化结果表明其中3个气孔为超标缺陷,其余2个气孔为允许存在的缺陷. 引入了三维剖切技术,在内表面发现了一个非超标的表面凹坑. 在三维重构模型的基础上,通过壁厚分析云图表征了焊缝区厚度分布的均匀性. 研究表明,该技术能高精度地对小管路焊缝内部缺陷进行定位、定量和定性分析.     

Bidirectional solidification of radial-type porous magnesium

Abstract

By use of the bidirectional solidification process of metal-gas eutectics, at an atmosphere of high-pressure hydrogen or gas mixture of hydrogen and argon, a special type of porous metal with radial pore distribution can be fabricated. During the bidirectional solidification of metal-gas eutectics, the volume of the solidifying metal expands due to the evolution of gas pores. This volume expansion leads to a severe transverse convection in front of the solidification interface. This paper studies the effect of solidification condition on porosity, pore size and distribution, and the depression and/or elimination of transverse convection. The results show that during the solidification, the transverse convection in front of the solidifying interface will affect the growth direction of the gas pores, promote gas bubble escaping, and degrade the uniformity of gas pore distribution. These effects of convection are influenced by the structure of casting mould. By properly designing the structure of the casting mould, the severe transverse convection in front of the solidification interface can be depressed or limited to a lower level, and high quality radialtype porous magnesium with uniform pore distribution can be obtained.     

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.     

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.     

B4C/Al中子吸收板腐蚀过程中的起泡研究

根据亨利定律,建立了B4C/Al中子吸收板包壳腐蚀起泡的模型,计算了孔隙半径、温度对起泡的影响,并利用孔隙毛细管效应分析了孔隙对中子吸收板起泡的影响.结果表明:孔隙半径越小,腐蚀产生的氢气压力越大,B4C/Al中子吸收板包壳更易起泡;温度对腐蚀产生的氢气压力影响非常小,而孔隙半径是影响氢气压力的主要因素;氢气持续产生并在孔隙毛细管中积聚,是包壳产生起泡的动力;水分容易通过孔隙毛细管在B4C/Al芯体中扩散,可导致Al腐蚀,引起包壳起泡.     

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.     

Pore structure and mechanical properties of directionally solidi ed porous aluminum alloys

Porous aluminum alloys produced by the metal-gas eutectic method or GASAR process need to be performed under a certain pressure of hydrogen, and to carry over melt to a tailor-made apparatus that ensures directional solidif ication. Hydrogen is driven out of the melt, and then the quasi-cylindrical pores normal to the solidif ication front are usually formed. In the research, the effects of processing parameters(saturation pressure, solidif ication pressure, temperature, and holding time) on the pore structure and porosity of porous aluminum alloys were analyzed. The mechanical properties of Al-Mg alloys were studied by the compressive tests, and the advantages of the porous structure were indicated. By using the GASAR method, pure aluminum, Al-3wt.%Mg, Al-6wt.%Mg and Al-35wt.%Mg alloys with oriented pores have been successfully produced under processing conditions of varying gas pressure, and the relationship between the f inal pore structure and the solidif ication pressure, as well as the inf luences of Mg quantity on the pore size, porosity and mechanical properties of AlMg alloy were investigated. The results show that a higher pressure of solidif ication tends to yield smaller pores in aluminum and its alloys. In the case of Al-Mg alloys, it was proved that with the increasing of Mg amount, the mechanical properties of the alloys sharply deteriorate. However, since Al-3%Mg and Al-6wt.%Mg alloys are ductile metals, their porous samples have greater compressive strength than that of the dense samples due to the existence of pores. It gives the opportunity to use them in industry at the same conditions as dense alloys with savings in weight and material consumption.     

用金属/气体共晶二维定向凝固法制备放射状规则多孔Mg

采用热传导方向为径向的金属一气体共晶二维定向凝固方法（二维Gasar）,在纯氢和氢、氩混合气氛下制备了气孔沿径向规则分布的放射状多孔金属Mg．研究了放射状多孔金属结构的特点以及气体压力等工艺参数对孔隙率、孔径和气孔分布的影响．结果表明,在圆柱形试样的二维定向凝固过程中,金属一气体共晶形成的体积膨胀会在凝固前沿的液相中产生大的对流,影响气孔的生长方向和规则程度,同时还会导致气体的逸出．随混合气体中氩气分压的增大,逸出程度下降;当氩气分压大于氢气分压时,气体的逸出被完全抑止．由此可以准确地预测出放射状规则多孔金属的孔隙率．