Influence of Compaction Conditions on the Foamability of AlSi8Mg4 Alloy

Aluminum AlSi8Mg4 alloy foams were produced by the powder compact foaming route using different parameters for the uniaxial powder compaction step. Compaction time, pressure, and temperature were varied and were found to influence both the density of the foamable precursor and the peak expansion reached during foaming. While peak expansion cannot be related to any single pressing parameter alone in a simple way, a clear dependence of expansion on the precursor density was found. Densification to a relative density between 97.5 and 99 pct yielded volume expansions of the foam up to 880 pct. Lower densities result in weaker foaming, due to insufficient encapsulation of the blowing agent; in addition, we were surprised to find that higher densification also has an adverse effect on peak expansion, most likely due to the elimination of nucleation centers or the effect of entrapped compressed air. Precursor microstructures were analyzed to identify the mechanisms leading to the observed density dependence of expansion.     

Fabrication of Aluminum Foams with Small Pore Size by Melt Foaming Method

This article introduces an improvement to the fabrication of aluminum foams with small pore size by melt foaming method. Before added to the melt, the foaming agent (titanium hydride) was pretreated in two steps. It firstly went through the traditional pre-oxidation treatment, which delayed the decomposition of titanium hydride and made sure the dispersion stage was controllable. Then such pre-oxidized titanium hydride powder was mixed with copper powder in a planetary ball mill. This treatment can not only increase the number of foaming agent particles and make them easier to disperse in the melt, which helps to increase the number of pores, but also reduce the amount of hydrogen released in the foaming stage. Therefore, the pore size could be decreased. Using such a ball-milled foaming agent in melt foaming method, aluminum foams with small pore size (average size of 1.6 mm) were successfully fabricated.     

PCM法泡沫铝合金的研究现状

介绍了泡沫铝的国内外研究现状和改善泡沫铝合金性能的途径,讨论了一些因素对PCM法制备泡沫铝发泡行为及其孔结构的影响。这些因素包括预制体制备方式、粉体颗粒粒度、TiH2的分解特性和冷却方式。并对PCM法制备泡沫铝合金今后的发展方向和现存问题做了分析。     

泡沫铝制备与其压缩性能研究

采用粉末致密化发泡（PCF）工艺制备了泡沫纯铝,对制备过程及影响孔结构的因素进行了分析.系统研究了压力、发泡温度、发泡时间、发泡剂含量和粒度对泡沫纯铝结构变化的影响规律,用自行设计的软件FoamScan对孔结构进行了描述.得出了试验条件下的优化工艺参数配置.进行了泡沫铝压缩性能测试,通过理论模型、性能测试数据作图对比的方法获得了孔隙率83%～87%泡沫纯铝的屈服强度表达式.确定了泡沫纯铝的制备工艺、结构、性能的相互关系.     

About the foamability of iron - carbon alloys

The foamability of iron-carbon alloys using the powder metallurgical process route was investigated. Pure iron and carbon powder with an addition of foaming agent were mixed and compacted. The foaming process started during heating the sample as soon as a temperature above the solidus temperature of the iron-carbon alloy was reached. Result of the process is an iron foam with a porosity of up to 60%. It was investigated, how the foaming behaviour is influenced by the parameters of alloy composition and compaction process. Different foaming agents (alkaline earth metal carbonates and metal nitrides) as well as different carbon additions and compacting processes were tested. It can be seen that sort and amount of foaming agent have an unexpected low influence on the expansion process whereas an increasing carbon content supports the expansion significantly. The use of different compacting processes has only little influence on the expansion itself, but highly effects both the pore distribution and homogeneity. The poor effect of the foaming agent cannot be satisfactorily explained. Investigations of a possibly premature gas emission or of a not gas-tight inclusion of the foaming agent do not show clear results. The support of the expansion by carbon additions can be attributed to the formation of CO-gas by the Vacher-Hamilton law during simultaneous formation of the liquid Fe-FeC-eutectic phase. The more inhomogeneous pore structure of iron foams caused by the use of hot-or hot isostatically pressed semi-finished products can be traced back to a higher internal gas pressure in the sample which results in a burst of the microstructure of the semi-finished product.     

Evaluation of mechanical properties of porous 6061 alloys fabricated by the powder compression and induction heating process

The purpose of this study is to evaluate the mechanical properties of 6061 Al foam products, which were fabricated by the powder compression and multistep induction heating method, and to build the database necessary for computer-aided modeling or foam components design. In this study, 6061 Al foams with various porosity fractions were fabricated according to the porosity fractions-final heating temperature curve. The relationships between porosity fraction and morphological properties (porosity diameter, number per unit area of porosities, and surface skin thickness) were investigated. Mechanical properties such as compressive strength, energy absorption capacity, and efficiency were investigated to evaluate the feasibility of foams as crash-energy-absorbing components. Furthermore, the effect of the surface skin thickness on the plateau stress and strain sensitivity of the 6061 Al foam with low porosities (pct) was studied.     

Reproducibility of Aluminum Foam by Combining Sintering and Dissolution Process with Precursor Foaming Process

A preliminary study of the reproducibility of aluminum foam was performed. Aluminum foam was fabricated by a sintering and dissolution process. It was found that aluminum foam containing a blowing agent can be fabricated without the decomposition of the blowing agent, namely, the densified aluminum foam can be used as a foamable precursor for refoaming. By heat treatment of the densified aluminum foam containing the blowing agent, pores were reproduced in the aluminum.     

基于PCM法泡沫铝制备工艺的控制及发展

介绍了粉末冶金压制法制备泡沫铝的国内外研究现状,讨论了一些因素对PCM法制备泡沫铝发泡行为及其孔结构的影响。并对PCM法制备大尺寸泡沫铝的工艺做了介绍。最后对PCM法制备泡沫铝合金今后的发展方向和现存问题做了分析。     

PCM法泡沫铝的研究及应用现状

介绍了PCM法制备泡沫铝的国内外研究现状，讨论了一些因素对泡沫铝发泡行为及其孔结构的影响。并对PCM法大尺寸泡沫铝及复合结构的制备、应用做了介绍。最后对PCM法制备泡沫铝今后的发展方向和现存问题做了分析。     

中频感应烧结和电阻炉烧结对钨坯组织及加工性能的影响

以加工离子注入机核心结构件所用的钨制品为研究对象,采用2400℃钨丝网真空-氢气烧结炉进行电阻炉烧结,对比研究中频感应烧结和电阻炉烧结的钨坯组织及加工性能。结果表明,采用电阻炉烧结可以改善钨坯的孔隙分布和形貌。在对电阻炉烧结的钨板坯进行深加工过程中,无掉角、掉边现象,表现出良好的加工性能。     

粉末烧结法制备开孔泡沫铝压缩性能的研究

采用粉末烧结工艺制备开孔泡沫铝并研究了其压缩性能，不同形态的尿素和氯化钠颗粒作为造孔剂使泡沫铝的孔隙度控制在70％。结果表明：粉末烧结法制备的泡沫铝呵以容易地控制孔隙度及孔径的大小，并且孔结构很好地保持了造孔剂的形状。不同的孔结构对泡沫铝的压缩性能具有显著影响，球形孔结构得到了最佳的压缩效果。     

Preparation of high porosity metal foams

Metal foams with porosities greater than 90 pct were prepared by a novel powder metallurgy route using a polymeric vehicle. Coarse titanium powder and fine carbonyl iron powder were tested. The powders were blended with each component of a two-part polyol-isocyanate foaming system, and the resulting suspensions were mixed and allowed to expand. Although the resulting polymer-metal foam was closed cell, particles were not retained in the windows. Upon pyrolysis to remove the resin, the windows opened and the final sintered metal foam was reticulated. Such foams present very low sintered density and are correspondingly weak after sintering but offer a fine reticulated structure with cell diameters in the region of 100 to 200 μm. They may have applications in the areas of catalysis, biomaterials, and composites.     

高温用（SiC—AlN）Mo功能梯度材料的加工

讨论了热屏蔽用（SiC－AIN）／Mo功能梯度材料的粉末冶金加工。利用钼作为基体材料，以承担结构强度和连接可能性。根据在1000K温差内的完全热传递，研究了组分配置的设计，并且以最佳的组分配置成功地加工出了（SiC－AIN）／Mo功能梯度材料的烧结坯料。     

Fabrication of Al-3.7?Pct Si-0.18?Pct Mg Foam Strengthened by AlN Particle Dispersion and its Compressive Properties

Al-3.7 pct Si-0.18 pct Mg foams strengthened by AlN particle dispersion were prepared by a melt foaming method, and the effect of foaming temperature on the foaming behavior was investigated. Al-3.7 pct Si-0.18 pct Mg alloy containing AlN particles was prepared by noncompressive infiltration of Al powder compacts with molten Al alloy in nitrogen atmosphere, and it was foamed at different foaming temperatures ranging from 1023 to 1173 K. The porosity of prepared foam decreases and the pore structure becomes homogeneous with increasing foaming temperature. When the foaming temperature is higher than 1123 K, homogeneous pores are formed in the prepared ingot without using oxide particles and metallic calcium granules, which are usually used for stabilizing a foaming process. This stabilization of the foaming at high temperatures is possibly caused by Al₃Ti intermetallic compounds formed at high temperature and AlN particles. Compression tests for the prepared foams revealed that the absorbed energy per unit mass of prepared Al-3.7 pct Si-0.18 pct Mg foam is higher than those of aluminum foams strengthened by alloying or dispersion of reinforcements. It is remarkable that the oscillation in stress, which usually appears in strengthened aluminum foams, does not appear in the plateau stress region of the present Al-3.7 pct Si-0.18 pct Mg foam. The homogeneity in cell walls and pore morphology due to the stabilization of pore formation and growth by AlN and Al₃Ti particles is a possible cause of this smooth plateau stress region.     

LF炉埋弧渣的研究及应用

在实验室研究了中高碱度的两个基础系内加入不同发泡剂后的发泡性能，并在２５０吨钢包炉上进行了埋加热的工艺试验，据此对发泡机理，影响炉渣发泡的因素，加热工艺及埋弧加热对钢水和炉渣成分的影响进行了分析讨论。     

Modeling and processing of liquid-phase-sintered γ-TiAl during high-density infrared processing

A new method for the rapid processing of thin gage sheet of traditionally difficult-to-process materials, such as γ-TiAl, has been modeled and experimentally developed. The method uses high density infrared (HDI) rapid heating of a plasma arc lamp to liquid-phase sinter powder metal compact precursors to structures of varying densities. Material properties for precursor γ-TiAl compacts were effectively chosen or determined and then used with a finite-volume heat-transfer modeling code to model the process. With the aid of the model, processing parameters were determined that allowed for a temperature gradient across the sheet that would produce a liquid-phase cast structure on the surface, residual powder on the backside, and a middle layer solid + liquid zone. Temperature and phase fields were predicted through the thickness of the sheet using the model. Fine grain, lamellar structured materials were produced in the liquid-phase-sintered zone.     

高温反应合成TiAl金属间化合物的研究

研究了以自蔓延高温合成(SHS)技术合成TiAl金属间化合物的燃烧反应过程及有关工艺参数(受热温度、压坯密度、加热速率和原始粉末粒度)对反应合成TiAl金属间化合物的影响。研究结果表明,Ti与Al之间的剧烈放热反应是在Al熔化之后产生的。当加热速率快时,压坯密度高较有利于燃烧反应的进行及TiAl金属间化合物的合成。加热速率和Al粉粒度对燃烧反应过程的影响与预燃烧相的形成有关。     

泡沫铝及其三明治结构累积叠轧制备

通过累积叠轧法制备泡沫铝.采用称重法研究泡沫铝孔隙结构,利用光学显微镜观察泡沫铝孔隙形貌.发现以TiH₂为发泡介质,当发泡温度660~680℃和发泡时间6~10 min时,利用累积叠轧法制备泡沫铝的孔隙结构特性最好.发泡温度和发泡时间的最佳值与发泡剂用量有关,TiH₂质量分数为1.5%,在670℃发泡8 min,泡沫铝的孔隙率可达到42%,孔径为0.43 mm.以制备的泡沫铝为夹芯,通过轧制复合制备了TC4钛合金/泡沫铝芯和1Cr18Ni9Ti不锈钢/泡沫铝芯三明治板.利用光学显微镜和能谱仪研究了三明治板的界面.面板与芯板间的化合反应形成了界面的反应层,界面实现了冶金结合.      

Densification behavior of dynamically shock compacted AI2O3/ZrO2 powders synthesized through rapid solidification

The rapidly solidified alumina-zirconia eutectic contains high volume fractions of nanocrystallinet- ZrO₂, which makes the material a promising precursor for the manufacturer of fracture-resistant ceramic specimens. Unfortunately, conventional powder processing and sintering techniques are inadequate for the fabrication of dense specimens using this material. We have used dynamic shock compaction to facilitate the achievement of high density specimens which retain the unique microstructure of the precursor material. In an attempt to quantify the dynamics of the microstructural evolution which occurs during the compaction process, we have investigated the effect of various particle size distributions on the densification behavior of the material during the shock compaction and postcompaction sintering cycles. The shock compaction process produced high densities (∼73 to 78 pct of single-crystal theoretical) by inducing a highly efficient packing of the particles. A bimodal powder distribution was also compacted and this specimen exhibited a relative density of 86.2 pct, approximately 10 pct higher that those of the unimodal compositions. In this compact, the small particles efficiently filled the interstices between the larger particles. The high density of the bimodal compact did not translate to a high sintered density, however. This article is based on a presentation made in the symposium “Dynamic Behavior of Materials,” presented at the 1994 Fall Meeting of TMS/ASM in Rosemont, Illinois, October 3-5, 1994, under the auspices of the TMS-SMD Mechanical Metallurgy Committee and the ASM-MSD Flow and Fracture Committee.     

Effect of Sn on the Dehydrogenation Process of TiH2 in Al Foams

The study of the dehydrogenation process of TiH₂ in aluminum foams produced by the powder metallurgy technique is essential to understanding its foaming behavior. Tin was added to the Al foam to modify the dehydrogenation process and stabilize the foam. A gradual decomposition and more retention of hydrogen gas can be achieved with Sn addition resulting in a gradual and larger expansion of the foam.