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.     

尿素作为造孔剂制备泡沫钛的结构和力学性能

采用针状尿素作为造孔剂,在造孔剂含量介于60%~80%的情况下进行了泡沫钛的制备。通过造孔剂技术成功地制备出孔隙率介于50.2%~71.4%的泡沫钛。扫描电镜结果表明,孔的连通程度随着造孔剂含量的增加而增加,当造孔剂含量超过70%时形成开孔泡沫钛。力学性能测试结果表明,力学性能随着孔隙率的增加而减小,试样的屈服强度、抗压强度和杨氏模量分别介于34.4~146.8 MPa、40.6~193.2 MPa和0.5~3.3 GPa。孔隙率为50.2%和71.4%的泡沫钛的杨氏模量分别匹配于皮质骨和松质骨的模量,理论上可作为潜在的骨替代材料。     

Preparation and characterization of porous titanium using space-holder technique

Titanium-based porous materials can be used in structural applications and medical implants because of their excellent mechanical properties at elevated temperatures, good corrosion resistance and wonderful biocompatibility. However, most of the methods used to produce the po-rous metal can only give limited porosity and uncontrollable pore morphologies. In the present study, a newly developed method of powder metallurgy using the space-holder technique was used to fabricate porous titanium with controllable porosity. The morphological features and mechanical properties of the products were fully investigated. The results show that the porosity is in the range of 55%-75%, and the mean pore size, with an average sphericity of～0.72, is 600 μm The plateau stresses vary between 10 MPa and 35 MPa. As predicted by the Gibson-Ashby model, the plateau stress decreases with increasing porosity.     

占位剂K2SO4对NiCu合金多孔膜孔结构的影响

以Ni元素粉末为原料,K₂SO₄粉末为占位剂,将Ni-K₂SO₄混合粉末加入聚乙烯缩丁醛(PVB)乙醇溶液中制成浆料,刮涂在Cu箔上,利用Kirkendall效应,经真空烧结制备多孔NiCu合金膜。研究K₂SO₄含量对NiCu合金多孔膜收缩率、透气度、孔径、宏观和微观形貌的影响。结果表明:随Ni-K₂SO₄混合粉末中的w(K₂SO₄)增加,多孔膜的透气度先增大后减小。当w(K₂SO₄)<40%时,随w(K₂SO₄)增加,膜层的烧结收缩率减小,透气度增大,最大达到2361 m3/(m2·h·kPa),最大孔径在45μm左右变化不大;w(K₂SO₄)大于40%时,多孔膜的透气度下降,孔径明显减小;当w(K₂SO₄)>60%,膜层透气度低于测试仪器下限。适量的K₂SO₄通过在涂覆层中的占位作用阻碍Ni颗粒烧结致密化,提高多孔膜的透气度,但过量的K₂SO₄会在烧结过程中阻断Cu原子向Ni粉层扩散,使Cu箔上难以形成通孔,透气度大幅降低。     

LOW DENSITY AND HIGH STRENGTH NiTi MEMORY ALLOYS WITH CONTROLLABLE PORE CHARATERISTICS AND THEIR SUPERELASTICITY

采用球形尿素颗粒预造孔工艺结合梯级粉末烧结方法制备出孔形规则、孔径大的轻质高 强多孔NiTi形状记忆合金. 通过控制造孔剂(尿素)的含量可有效调节多孔合金的孔隙特征, 获得孔径均匀、孔形圆整和孔隙率可控的样品, 其中孔径为296-732 um, 孔隙率为31%-61.6%; 尿素形状和尺寸对多孔合金的孔隙特征有决定性影响, 具 有几何形态遗传性; 尿素对多孔NiTi合金的组成相影响很小, 相变仍具有马氏体相变特征; 合金具有优良的力学性能和稳定的线性超弹性.     

Pore structures of high-porosity NiTi alloys made from elemental powders with NaCl temporary space-holders

The unusual pseudo-elasticity and shape memory effect make NiTi alloys promising energy absorption materials. In the present study, powders of Ti, Ni and NaCl particles were mixed and cold-pressed into green ingots and green ingots were then desalted and sintered in vacuum to form high-porosity NiTi alloy specimens with porosity up to 90%. Microstructure observation shows that two kinds of pores with sizes of 200-400 μm and 10-50 μm respectively are well-distributed in these high-porosity NiTi alloys. Characteristics of pores were studied and formation mechanism was discussed.