This paper reviews the recent development of fabrication methods of porous metals with open-channels. The open-channel metals are fabricated through powder sintering or solidification technique. The template wires are embedded in the sintered or solidified metals, such as aluminum, copper, titanium and its alloys, which are then removed by chemical dissolution or extraction methods. The hole size, hole length and porosity are uniquely controlled by thickness, length and number of template metallic wires, respectively. The pore size ranges from 102 to several 103 μm in diameter. The open-channel metals are characterized by a large aspect ratio of the length to the diameter of the holes in metals. Furthermore, the techniques can fabricate spiral and V-shaped pores in metals. Feasibility and usefulness of each fabrication method are discussed. The methodology for producing the open-channel metals is expected to provide expanded opportunities for application technologies such as functional materials like heat sinks and sound absorbers and light-weight structural materials.

The adoption of selective laser melting (SLM) for fabrication of porous titanium has resulted in many new investigations into the complex design parameters associated with porous architecture of high spatial resolution. The development of meta-materials has included research into the effects of unit cell architecture (strut versus sheet), porosity, pore size, and other factors on the performance of metallic scaffolds. The current study examined the interactive effects of varying the gyroid sheet unit cell size and overall specimen size on the compressive behavior of Ti–6Al–4V ELI porous scaffolds manufactured via SLM. The increasing unit cell size relative to specimen geometry was found to decrease the compressive strength and stiffness of the overall structure and shift the material fracture mode. The understanding of the relationship between unit cell size and specimen geometry can be used to optimize mechanical properties of implants with constrained volumes and pore/wall size requirements to optimize properties of porous titanium implants for strength and osseointegration.

Porous metals represent a class of materials where the interplay of ligament length, width, node structure, and local geometry/curvature offers a rich parameter space for the study of critical length scales on mechanical behavior. Colloidal crystal templating of three-dimensionally ordered macroporous (3DOM, i.e., inverse opal) tungsten provides a unique structure to investigate the mechanical behavior at small length scales across the brittle–ductile transition. Micropillar compression tests show failure at 50 MPa contact pressure at 30 °C, implying a ligament yield strength of approximately 6.1 GPa for a structure with 5% relative density. In situ SEM frustum indentation tests with in-plane strain maps perpendicular to loading indicate local compressive strains of approximately 2% at failure at 30 °C. Increased sustained contact pressure is observed at 225 °C, although large (20%) nonlocal strains appear at 125 °C. The elevated-temperature mechanical performance is limited by cracks that initiate on planes of greatest shear under the indenter.

In this paper, CNTs reinforced foam aluminum matrix composites with small pore diameter were prepared by powder metallurgy method. When the mass fraction of CNTs was 0.75%, the tensile strength, flexural strength and compressive yield strength of the materials were 3.4 times, 2.4 times and 2.4 times of pure foam aluminum, respectively, reaching the maximum value, which obviously improved the mechanical properties of aluminum foam. The tensile property model of foam aluminum matrix composites was built to predict the properties of the composites, and the effects of defects and reinforcement on the mechanical properties of the composites were compared. The results show that the tensile fitting is consistent with the measured results when the mass fraction of CNTs is less than 0.75%, but the weakening effect of defects on the strength of aluminum foam is much greater than the enhancement of CNTs. With the increase of CNTs mass fraction, the damping loss factor of foam aluminum composites increases, dislocation damping and grain boundary damping play a role in advance, and the damping peak moves to the low temperature region.

In this study, the quasi-static and dynamic mechanical behaviors and the energy absorption capacity of closed-cell aluminum foams with uniform and graded densities were experimentally studied. The effects of density, strain rate, and graded density on the mechanical performances of aluminum foams were quantitatively evaluated. It was shown that the density had a significant effect on the quasi-static and dynamic compressive stress of aluminum foams. Moreover, impact compression experiment results revealed that aluminum foam was sensitive to the strain rate. As the strain rate increased, the plateau stress and energy absorption capacity increased distinctly and the rate of deformation increased correspondingly. Finally, the investigation of aluminum foams with uniform and graded densities to study their deformation and failure mechanisms, mechanical characteristics, and energy absorption capacities showed that the GD 0.48-IV specimen exhibited superior impact resistance. The present work can provide a valuable reference for the optimum design of aluminum foam against impact loading.

Iron foams are potential materials for the production, purification, and recuperation of hydrogen through redox systems. They are inexpensive, recyclable, and environmentally friendly. Nevertheless, iron foams cannot be employed repeatedly for redox cycling at high temperatures because the structure suffers morphological changes and a decrease in the effective porosity. In this work, two different pore structures of Fe-foams fabricated by freeze-casting have been produced: constant (CP) and gradient (GP) pore size. CP Fe-foams were obtained by employing a double-sided cooling technique to minimize gradients in pore width that result when using one-sided, constant cooling solidification techniques. GP Fe-foams were manufactured using a fixed-temperature cold plate. Optical microscopy and X-ray tomography were employed to characterize the pore structure and, for GP Fe-foams, to investigate the effect of redox cycling. After redox cycling, GP Fe-foams exhibited significant pore degradation.

Novel three-dimensional (3D) hierarchical macro- to nano-porous titanium (Ti) and TiMo alloys with sufficient compressive strength (CS) were prepared using NaCl spacer and dealloying methods. The dealloying process was implemented by the heat treatment of TiCu and TiMoCu master alloys in Mg powders. The 3D-hierarchical porous structures were composed of large pores having a mean size of 400 μm with interconnected micro-pores in the size of 10–30 μm, where the pore walls possessed numerous nano-pores with a size range of 10–50 nm. The CS and elastic modulus values were 72.4 MPa and 2.67 GPa as well as 92.62 MPa and 3.36 GPa for Ti and TiMo, respectively. The hierarchical porous structure is beneficial for the fast nucleation of bone-like apatite after immersion in simulated body fluid (SBF). In addition, TiMo samples after NaOH and heat treatments provide better apatite formation after soaking in SBF for a week, in comparison with the samples without treatment.

In this article, Al75Cu25 (at.%) ribbons were dealloyed by HCl, H2C2O4, H3PO4, and NaOH solutions, respectively, to prepare nanoporous copper (NPC). The dealloying behavior is varied with dealloying solutions, allowing modulating the microstructure and porosity of the NPC. Al75Cu25 ribbons are fully dealloyed in HCl, H2C2O4, and NaOH solutions, whereas they are partially dealloyed in H3PO4 solution. Except the NPC prepared in the NaOH solution, no obvious cracks are traced in other samples. The surface diffusivity (Ds) of Cu atoms along the alloy/solution interfaces is varied with solutions, producing the NPC with different microstructure. NPC with higher specific surface area can be obtained by dealloying the Al75Cu25 ribbons in the HCl solution. Compared with the dealloying in H2C2O4, H3PO4, and NaOH solutions, the dealloying in 10 wt% HCl solution for 25 min at 90 ± 1 °C facilitates the best NPC in this work.

In this study, uniaxial tensile loading simulations were performed on several single crystalline copper nanoporous (NP) structures with varying relative density (RD) via molecular dynamics simulations. From the results, two distinctive deformation patterns were observed: structures with a low RD went through coarsening, and structures with a high RD did not. During coarsening, dislocations are nucleated because of the high surface stress induced by the thin ligaments. These dislocations drive the merging of ligaments as well as nodes and lead to an increase in the differences between the size of nodes and ligaments. The disproportional nodes and ligaments result in a lowered strength. In addition, larger nodes provide more favorable circumstances for the formation of sessile dislocations, which hinder the movement of other propagating Shockley partials and result in strain hardening. Subsequently, lower RD structures offer anomalously high strain-hardening potential, whereas high RD structures show better strength but poor deformability. These results help us in better understanding the plastic behavior of NP structures as a function of their RD.

Metallic thin-film composite membranes are produced by sputtering metal films onto commercial polymer membranes. The separations capability of the membrane substrate is enhanced with the addition of a 10 nm Ta film. The addition of a tantalum layer decreases the molecular weight cutoff of the membrane from 70 kDa dextran (19 nm) to below 5 kDa (6 nm). Water flux drops from 168 LMH/bar (LMH: liters/meters2/hour) (polymer support) to 8.8 LMH/bar (Ta composite). A nanoporous layer is also added to the surface through Mg/Pd film deposition and dealloying. The resulting nanoporous Pd is a promising catalyst with a ligament size of 4.1 ± 0.9 nm. The composite membrane's ability to treat water contaminated with chlorinated organic compounds (COCs) is determined. When pressurized with hydrogen gas, the nanoporous Pd composite removes over 70% of PCB-1, a model COC, with one pass. These nanostructured films can be incorporated onto membrane supports enabling diverse reactions and separations.