Fabrication and compressive behavior of open-cell aluminum foams via infiltration casting using spherical CaCl2 space-holders

The infiltration casting fabrication process based on spherical CaCl₂ space-holders and the compressive behavior including the mechanical performance and energy absorption capacity of open-cell aluminum foams were investigated.Open-cell aluminum foams with different porosities in the range of 63.1%to 87.3%can be fabricated by adjusting compression ratios of CaCl₂ preforms prepared by precision hot-pressing.The compression tests show that a strain-hardening phenomenon always occurs especially for open-cell aluminum foam with low porosity,resulting in the inclining stress-strain curve in the plateau region.The energy absorption capacity of open-cell aluminum foam decreases with increasing porosity when compared at the same strain.However,when compared at a given stress,each foam can absorb the maximal energy among the five foams in a special stress range.Additionally,open-cell aluminum foam possesses the maximum energy absorption efficiency at its optimum operating stress.At this stress condition,the foam can absorb the highest energy compared with other foams at the same stress point.The optimum operating stress and the corresponding maximal energy absorption decrease with increasing the porosity.The optimum operating stress for energy absorption can also be determined similarly when taking into consideration of the lightweight extent of foams.     

Preparation of porous Ti35Nb alloy and its mechanical properties under monotonic and cyclic loading

The Ti-35%Nb(mass fraction) foams were prepared by a powder metallurgy method,and the microstructure and the mechanical properties of the foams under monotonic and cyclic loading were investigated.The microstructure of the foams mainly consists of β phase,and the foams exhibit the homogenous pore distribution with the average pore size of 252 μm.The foams with 66% porosity show a typical stress-strain curve of the open-cell foams,and the plateau stress is about 56 MPa.The fatigue strength of the foam is 15.12 MPa at 107 cycles.The fractographic analysis of the foams reveals that the cracks nucleate within the struts and grow in a fatigue mechanism,resulting in the acceleration of the fatigue damage of the foams.     

添加造孔剂法制备开孔泡沫铝及其性能研究

以球形尿素颗粒为造孔剂,采用传统的粉末冶金工艺制备开孔泡沫铝并研究了其性能.结果表明,添加造孔剂法制备的泡沫铝可以任意控制孔隙率及孔径的大小,且孔结构良好,保持了造孔剂的形状;高的烧结温度使泡沫铝的压缩强度提高,但过高的温度将导致孔壁熔化.本试验制成的泡沫铝其压缩曲线和泡沫金属典型压缩曲线相似,且抗压强度和经典理论计算结果一致.     

开孔泡沫金属热传导性能的理论研究与数值模拟

基于Ashby的规则正立方体单胞模型,研究了轻质泡沫金属材料的拓扑构型(孔隙率和孔径大小)对其热传导性能的影响。利用最小热阻法推导了开孔泡沫金属气固两相的等效热传导系数的表达式,并首次采用简化的积分方法,得到了等效热传导系数的近似解析解。应用ABAQUS有限元分析软件模拟了开孔泡沫金属横断面的热流密度分布和稳态热传导Fourier定律,分析了不同孔隙率和孔径大小开孔泡沫材料的热传导性能。结果表明,多孔泡沫金属的热传导系数随着孔隙率的增大而线性减小,且当孔隙率保持恒定时,热传导系数与孔径的大小无关。理论分析和数值模拟结果吻合较好。研究结果对多孔金属的工程应用具有重要的参考价值。     

Performance of stainless steel foams produced by infiltration casting techniques

Ferritic (AISI 430) and austenitic (AISI 304) stainless steel foams were produced exploiting a process based on molten metal infiltration on ceramic model. In particular, SiC foundry filter was used as space holder and, after the solidification, it has been removed by hydrofluoric acid. The produced foams are featured by three different porosity grades (10, 20 and 30 PPI) and by constant relative density (0.60). The morphology, the mechanical properties and the corrosion resistance were studied and the results were correlated to the material, the porosity, the size and the distribution of the voids. Morphologically, the structure is arboreous open-cell foam featured by interconnected cavities. This aspect, combined with the high relative density, assures high compressive plateau stress, structural integrity and good deformability. The corrosive tests, according to the ASTM A262-Met.B and NACE TM-0284, permitted to identify possible application fields for these products.     

石膏型渗流法制备的开孔泡沫铝的压缩行为研究

本文采用可溶石膏型预制块,通过加压渗流的方法制备了泡沫纯铝、泡沫ZL101合金和泡沫ZL102合金,并通过准静态压缩实验研究了3种不同基体材料的泡沫铝的压缩行为及吸能性能.结果表明:通过石膏型渗流法制备的开孔泡沫铝合金的孔隙率可以达到85％～93.5％;泡沫铝基体材料的力学性能对泡沫铝压缩力学性能有重要影响;泡沫ZL1...     

高温固相扩散处理对开孔泡沫Fe-Ni力学性能的影响

采用高温固相扩散处理对开孔泡沫Fe-Ni进行合金化,研究了不同处理温度,不同保温时间对泡沫Fe-Ni压缩性能及能量吸收特性的影响。采用扫描电镜(SEM)对合金化后的泡沫Fe-Ni进行形貌观察,并利用线扫描分析合金化前后两种元素的扩散情况;对合金化前后的泡沫Fe-Ni进行了纳米压痕试验和准静态压缩试验,研究了泡沫Fe-Ni网丝硬度、准静态压缩力学行为及其吸能性。结果表明:经高温固相扩散处理后,泡沫Fe和Ni镀层界面上发生了Fe-Ni的互扩散,形成(Fe,Ni)无限固溶体结构;随着温度升高,保温时间增长,Fe、Ni元素分布更趋于均匀化,泡沫Fe-Ni网丝平均纳米硬度值更高。1200℃高温固相扩散2h后泡沫Fe-Ni平台区应力值增加,平台区长度增加。泡沫Fe-Ni吸能能力整体趋势随应变的增加而线性增大。其中,1200℃高温固相扩散保温2h,泡沫Fe-Ni能量吸收值比合金化前提高了31.9%。     

A novel technique for making open-cell AI203-ZrO2 ceramic foam with plant seed template

The aim of the present research is to provide a technique for preparing open-cell AI203-ZrO2 ceramic foams with uniform cell size. This technique used plant seeds to array templates and centrifugal slip casting to obtain cell struts with high packing density. Aqueous Al2O3-ZrO2 slurries with up to 50 vol.% solid contents were prepared and the rheological characteristic of the slurries was investigated. Consolidation was performed at an acceleration of 2,860 g for 60 rain. The effect of the characteristic of plant seeds on the drying behavior of Al2O3- ZrO2 green compact was analyzed. The effects of the solid contents of slurries on segregation phenomena ofAl2O3 and ZrO2 particles and green compact uniformity were investigated. The compressive stress-strain curve and deformation behavior of Al2O3-ZrO2 ceramic foams prepared using plant seed template were analyzed. The results showed segregation phenomenon is negligible for highly stable slurry with 50 vol.% solid loading. The prepared cell struts of Al2O3-ZrO2 foams have high green density (61.9% TD), sintered density (99.1% TD) and homogeneous microstructure. When sintered at 1,550 ℃ for 2 h, the cell size of Al2O3-ZrO2 foam is approximately uniform and the diameter is about 1.1 mm. The porosity and compressive strength of sintered products is 66.2% and 5.86 MPa, respectively.     

用于骨组织工程的镁基泡沫生物材料的制备与体外降解行为

采用熔体发泡法制备了一种镁基泡沫生物材料,其中以镁钙合金为基体材料,羟基磷灰石(HA)为增粘剂,以碳酸镁(MgCO3)为发泡剂。对结构均匀的镁基泡沫生物材料进行测试,研究其生物可降解行为。用腐蚀前后孔结构、浸泡试验和电化学测试对镁基泡沫材料的生物可降解性进行表征。结果表明,在固定时间内随着试样孔隙率的增加,失重率不断增加;相比于添加了羟基磷灰石(HA)的样品,不含HA颗粒地样品呈现出更高质量损失率。同时,Mg基泡沫生物材料的总孔隙率和羟基磷灰石(HA)含量均对Mg基泡沫材料的开孔率有重要的影响。在相同时间内,开孔率随试样总孔隙率的增加而增加。在模拟体液(SBF)介质中,含有羟基磷灰石(HA)的Mg基泡沫生物材料比不添加羟基磷灰石(HA)的试样具有更高的耐腐蚀性。     

Compressive deformation behavior and energy absorption characteristic of aluminum foam with elastic filler

An open-cell aluminum foam filled with silicate rubber (AFFSR) was fabricated by infiltration of the liquid silicate rubber into the open-cell aluminum foam. The experiments were carried out to investigate the compressive behavior and energy absorption characteristics of the material. It is found that the stress--strain response of the AFFSR exhibits five regions including two plateau regimes, which is quite different from the stress--strain curves of many unfilled metallic foams that usually exhibit three distinct regions. The plastic deformation of the AFFSR is prolonged because of the filled silicate rubber, compared with the aluminum foam without such a filler. The AFFSR also exhibits a higher energy capacity than the aluminum foam without filler. Additionally, for the prolonged plateau region in the stress--strain curve, the energy absorption efficiency of the AFFSR maintains a high level (above 0.6) over a wide strain range from 3% to 60%.     

开孔泡沫铝导电性的研究

本文采用加压渗流方法制备开孔结构的泡沫铝,并通过调整工艺参数改变泡沫铝的孔径和相对密度.采用“直流四端电极”法测量了不同参数泡沫铝的电阻,研究开孔泡沫铝的导电性随其相对密度和孔径的变化规律.实验结果表明：随着相对密度的提高,开孔泡沫铝的电导率增大,且电导率随相对密度的改变呈指数关系变化;当相对密度参数基本相同时,随着泡沫铝孔径的减小,由于在制备过程中产生的结构缺陷增多,其电导性下降.     

盐球渗透铸造法制备开孔泡沫铝的孔结构及压缩性能

使用圆盘造粒机制备近球形的NaCl颗粒,并将其用于渗透铸造制备开孔泡沫铝。盐球的平均抗压缩强度为3.9 MPa,在超声波清洗机中可在5 min内完全塌陷。通过控制热压烧结时间为0.5～2 h,热压温度700℃,可制备堆积密度在0.66～0.83 g/cm³的预制体。延长热压烧结时间会使开孔泡沫铝的孔径从0.48 mm增加到1.16 mm,孔隙率从64%增加到82%。压缩实验结果表明,不同孔隙结构下泡沫体的宏观变形特征基本相同,均表现出逐层塌陷的变形特征。此外,泡沫铝的致密化应变值、弹性模量、平台屈服应力和能量吸收能力均随着孔隙率的增加而降低。当孔隙率为64%时,能量吸收能力最大(15.0 MJ·m^-3)。     

闭孔泡沫铝的电磁屏蔽性能

采用粉末冶金发泡法制备闭孔泡沫铝,通过调整发泡剂含量、发泡温度、粘度、保温时间等手段,制得孔隙率可调、孔洞分布均匀的闭孔泡沫铝样品,并测试了不同孔隙率、孔径泡沫铝样品的电磁屏蔽性能.结果表明:在100～1000MHz内,泡沫铝的电磁屏蔽性能在60～90dB之间,且随着孔隙率、孔径的增加,泡沫铝的电磁屏蔽性能下降.     

CaCl2作为造孔剂制备泡沫青铜的结构和力学性能

以青铜粉为原料、CaCl_2为造孔剂,采用粉末烧结溶解法制备开孔泡沫青铜。通过改变造孔剂体积分数和粒径成功制备出孔隙率为70%~90%,孔径1~3mm的泡沫青铜试样。研究了孔隙率和造孔剂的关系以及孔隙率、孔径对泡沫试样力学性能的影响,并对其孔结构,相组成和微观形貌进行观察和分析。结果表明:泡沫青铜试样的塑性屈服平台应力随孔隙率增加而减小,当孔隙率为77%~89%时,对应塑性屈服平台应力为12.6~2.6MPa。当应变量为50%时,孔隙率为77%~89%的泡沫青铜单位体积能量吸收值(W)范围为6.21~0.91MJ/m~3。试样的理想吸能效率(I)都接近0.82,说明泡沫青铜可以作为一种理想的吸能材料。     

开孔泡沫铝的低温热导率测量及其低温蓄冷应用研究

新型材料的应用对低温装置的发展起具有重大意义。为提高低温蓄冷装置的温度均衡性,一种孔隙率为63%的开孔泡沫铝材料最近在一种低温蓄冷装置中进行了实验研究。实验测试了样品从50 K到170 K的热导率,测试结果显示开孔泡沫铝在测试温度区间内热导率随温度降低而升高,其平均值为22W·(m·K)~(-1)。实验测试了开孔泡沫铝热导率对采用泡沫铝低温蓄冷装置的性能的影响。蓄冷装置中采用的相变材料为氮。实验中主要测试值为蓄冷装置在降温过程和融化过程中的温度值。实验结果显示,此装置上、下部分的最大温差小于0.5 K,远小于不采用开孔泡沫铝时的温差。随着低温蓄冷装置热导率的提高,蓄冷装置上、下部温差以及单个温度测定的温度波动均减小。     

开孔泡沫Al-10%Mg合金的动态压缩行为的研究

用Hopkinson压杆实验装置对开孔结构的泡沫Al—10％Mg合金进行了动态压缩实验，在应变率为准静态、800s^-1和2000s^-1条件下测量了动态和准静态压缩应力—应变曲线，研究了这种铝合金泡沫的动态压缩行为，并分析了其应变率效应。结果表明：在动态和准静态压缩下，泡沫Al—10％Mg合金的压缩σ—ε曲线均表现出弹性变形段、平缓段和紧实段三阶段特征；泡沫Al—10％Mg合金具有明显的应变率敏感性，随应变速率的提高，相同应变量下的流动应力上升。     

Creep-buckling of open-cell foams

A repeating element composed of four cell struts in a pentagonal dodecahedron model is used to analyze the creep-buckling of open-cell foams. The solid making up the cell struts is assumed to follow power-law creep. As a result, the theoretical expression for describing the failure time for the onset of creep-buckling of open-cell foams under uniaxial compression is obtained. Theoretical results indicate that the creep-buckling of open-cell foams depends on their relative density and microstructural imperfection and the creep parameters of solid cell struts. Furthermore, a simple relationship between creep strain rate and failure time is proposed for the creep-buckling of open-cell foams and then compared to the existing experimental results; they agree well. In addition, cell-strut creep-buckling is the dominant failure mechanism when the imposed compressive stress is close to the elastic buckling strength of open-cell foams. However, cell-strut creep-rupturing is more likely to occur when the imposed compressive stress becomes smaller. Moreover, the transition of failure mechanism from cell-strut creep-buckling to cell-strut creep-rupturing is discussed.     

Behavior of a random hollow sphere metal foam

The quasistatic uniaxial compression behavior of both single hollow spheres and bulk metal foams comprised of the same hollow spheres is examined experimentally. The spheres are nominally the composition of a 405 stainless steel (Fe–12Cr), with a 2 mm outside diameter and 0.1 mm thick walls, and are sintered together to process the bulk foam. It is shown that to first order the bulk foam stress–strain behavior, Poisson effects, and densification may be understood on the basis of simple experiments performed on single spheres between parallel platens. These hollow sphere foams appear to behave similar to open-cell foams. Finite element modeling of finite compression of a single sphere lends further insight into the deformation process and the role of plastic bending and contact of cell walls during the process of densification.     

Investigation of electroless copper plating on polyurethane foam,as an initial step of open cell foam production process

Abstract

Coating of polymeric foams is known as a method for production of metallic foams, which produces foams with high volume of porosity and controllable pore size. In this research, this method was employed to produce open cell copper foam by use of polyurethane foam with an average pore size of 0.4?mm as the substrate. Since polyurethane foam as a non-conductive material is not able to be coated directly by electrolytic deposition, the substrate was initially metallised by electroless copper plating. In the electroless plating process, the effects of the main parameters such as bath chemical composition, solution pH and temperature on deposition rate and thickness of the coatings obtained were investigated. The results showed that the optimum condition of the process is obtained when CuSO₄ concentration in the deposition bath is 12?g?L^??1, pH is 13 and plating temperature range is 55–60°C.     

合金化对泡沫铝压缩力学行为的影响

采用Si、Mg及Cu元素进行合金化处理，制备了几种不同力学性能的开孔泡沫铝，通过准静态压缩实验研究了合金化对泡沫铝压缩力学性能与吸能特征的影响。实验结果表明，Si、Mg及Cu元素合金化处理能显著改变泡沫铝的应力-应变行为与吸能特征，使泡沫铝的屈服强度提高，吸能性大幅度上升。