Solid-state microcellular foaming (SSMF) process was used to produce porous chemical mechanical polishing (CMP) pads in a variety of pore size and porosity range, using a variety of thermoplastic polyurethane (TPU) resin hardness. By controlling the pore size, porosity, and pad hardness, one is able to manufacture CMP pads that offer tunable pad properties. A brief introduction to the SSMF manufacturing process and thereby, unique microstructures created is first addressed followed by inner layer dielectric (ILD) CMP results, describing the effects of top TPU foam sheet properties, such as hardness, pore size, and porosity on ILD removal rate (RR) and wafer defects. Softer TPU-based porous pads showed significantly lower wafer scratch counts, while only a moderate increase in the ILD RR was seen with increasing resin hardness for similar pore size and porosity pads. Pore size has insignificant influence on wafer defect count but has significant influence on the ILD RR profile. CMP pads made from small pore size foams cause a nonflat RR profile.

This paper presents recent results of foam extrusion of thermoplastic cellulose acetate (CA) using HFO 1234ze as low global warming blowing agent and talc as nucleating agent. Foam extrusion behavior, physical foam properties, and foam morphologies were studied in detail with respect to blowing agent concentration and talc content. Depending on these parameters, thermoplastic CA exhibits excellent foam extrusion performance with good expansion behavior at the die. Talc as nucleating agent results in homogeneous fine foam morphologies with closed cells [i.e., Fig. 3(3)]. Depending on the blowing agent content and talc content, average cell size ranges from 1 to 0.12 mm and foam density ranges between 100 and 400 kg/m3.

Stable, responsive and autofluorescent genipin-crosslinked chitosan–poly(vinyl pyrrolidone) hydrogels have been synthesized. Morphological characterization techniques such as scanning electron microscopy, environmental scanning electron microscopy, and in situ confocal laser scanning microscopy (CLSM), in both reflectance and fluorescence modes, have been compared for their suitability to characterize the network structure of these hydrogels. CLSM is shown to be the optimal technique owing to the facile generation of the three-dimensional porous architecture and extra topographical information while the sample is immersed in the aqueous solution to which it will find application. CLSM is used in both reflectance and fluorescence modes to follow morphology variation as a function of time during swelling. Conveniently, acquisition via reflectance produces images with a higher degree of structural detail than fluorescence, widening the application of this method to characterize hydrogels where addition of a fluorescent probe, which may alter the native structure, is undesired.

We have used a hydrogel templating technique followed by the subsequent evaporation of water present to fabricate porous cement and porous PDMS composites, and we have analyzed their sound absorption properties. All experiments were carried out with hydrogel slurries of broad bead size distributions. Porous PDMS and cement composites were produced with porosities of up to 80% and 70%, respectively. Scanning electron microscope analysis shows fibrous domains within the voids created by the hydrogel in the cement samples and open pore network in the PDMS composites of initial hydrogel content higher than 70 vol%. Sound absorption was improved with respect to control nonporous samples in all composites with porosities higher than 60 vol%, where an open pore structure was formed. The porous PDMS and porous cement produced by this method show better sound absorption at 200–400 Hz and 1200–1800 Hz frequency ranges when compared with the sound absorption in the intermediate frequencies range between 400 and 1000 Hz.

The development and characterization of pressure sensing porous nanocomposites are reported here. A thermoplastic polyurethane (TPU) was chosen as an elastomeric matrix, which was reinforced with multiwall carbon nanotubes (MWNTs) by high shear twin screw extrusion mixing. Porosity was introduced to the composites through the phase separation of a single TPU-carbon-dioxide gas solution. Interactions between MWNT and TPU were elucidated through calorimetry, gravimetric decomposition, conductivity measurements, and microstructure imaging. The piezoresistance (pressure–resistance) behavior of the nanocomposites was investigated and found to be dependent on MWNT concentration and nanocomposite microstructure. Mechanisms of piezoresistance in solid and porous nanocomposites are proposed.

Metal matrix syntactic foams are promising materials with high energy absorption capability. To study the effects of matrix strength on the quasistatic compressive properties of syntactic foams using SiC hollow particles as reinforcement, matrices of Al-A206 and Mg-AZ91 were used. Because Al-A206 is a heat-treatable alloy, matrix strength can be varied by heat treatment conditions, and foams in as-cast, T4, and T7 conditions were tested in this study. It is shown that the peak strength, plateau strength, and toughness of the foams increase with increasing yield strength of the matrix and that these foams show better performance than other foams on a specific property basis. High strain rate testing of the Mg-AZ91/SiC syntactic foams showed that there was little strain rate dependence of the peak stress under strain rates ranging from 10−3/s to 726/s.

Some hydrides that could replace TiH2 as the hitherto most suitable blowing agent for foaming aluminum alloys were investigated. Hydrides taken from the group MBH4 (M = Li, Na, K) and LiAlH4 were selected since these have not been studied in the past although their decomposition characteristics appear to be suitable. Foamable precursors of alloy AlSi8Mg4 were manufactured by pressing blends of metal and blowing agent powders. Powders, precursors and precursor filings were studied by mass spectrometry to obtain the hydrogen desorption profile. Foaming experiments were conducted with simultaneous x-ray radiographic monitoring. Two Li-containing blowing agents were found to perform well and can be considered alternatives to TiH2.

The 3D morphological evolution of titanium foams as they undergo a two-step fabrication process is quantitatively characterized through x-ray micro- and nano-tomography. In the first process step, a Cu–Ti–Cr–Zr prealloy is immersed in liquid Mg, where Cu is alloyed with Mg while a skeleton of crystalline Ti–Cr–Zr is created. In the second step, the Mg–Cu phase is etched in acid, leaving a Ti–Cr–Zr foam with submicron struts. 3D images of these solidified Ti–Cr–Zr/Mg–Cu composites and leached Ti–Cr–Zr foams are acquired after 5, 10, and 30 min exposure to liquid Mg. As the Mg exposure time increases, the Ti–Cr–Zr ligaments grow in size. The tortuosity loosely follows the Bruggeman relation. The interfacial surface distribution of these Ti-foams is qualitatively similar to other nano-porous metal prepared by one-step dealloying. The characteristic length of the Mg–Cu phase and pores are also reported.

This paper presents the effect of oxygen, nitrogen, and carbon concentration on the microstructure and properties of titanium foams produced with a powder metallurgy process. Oxygen and nitrogen reduce the ductility and increase the compression yield strength of CpTi foams. The effect of nitrogen appears to be similar to the effect of oxygen, a trend different from the ones reported in the literature for dense titanium in tension, where the effect of nitrogen is recognized to be significantly more important than the effect of oxygen. For carbon, the levels investigated were above the room temperature solubility limit of carbon in α-Ti and titanium carbides were observed in the microstructure. The volume fraction of carbides observed in the microstructure increased with carbon content. The effect of the carbides on the compression properties and ductility of the titanium foams is, however, small compared to the effect of oxygen and nitrogen.

Recent advances in multiscale manufacturing enable fabrication of hollow-truss based lattices with dimensional control spanning seven orders of magnitude in length scale (from ∼50 nm to ∼10 cm), thus enabling the exploitation of nano-scale strengthening mechanisms in a macroscale cellular material. This article develops mechanical models for the compressive strength of hollow microlattices and validates them with a selection of experimental measurements on nickel microlattices over a wide relative density range (0.01–10%). The limitations of beam-theory-based analytical approaches for ultralight designs are emphasized, and suitable numerical (finite elements) models are presented. Subsequently, a novel computational platform is utilized to efficiently scan the entire design space and produce maps for optimally strong designs. The results indicate that a strong compressive response can be obtained by stubby lattice designs at relatively high densities (∼10%) or by selectively thickening the nodes at ultra-low densities.

Open pore metal foams may be of interest as regenerators because of their large specific surface area and their high porosity. In this experiment, three aluminum foam samples (pore size 2–2.36 mm and around 65% porosity) were manufactured by the replication process. The volumetric heat transfer coefficient and number of transfer units (NTU) of the foams and a packed bed of steel ball bearings (2 mm diameter) were determined using a single-blow transient technique over the range 500 < Rem < 1400. The NTU values of the foams and ball bearings both reduced with increasing Reynolds number (flow velocity). The pressure drop across the matrices increased with the velocity, though the values for the metal foams were much lower than that of the ball bearings, indicating that they may have potential for this type of application.

Nanocasting into silica templates for preparation of mesoporous materials has up to now been limited to those metal oxides and metals that can withstand the harsh silica etching processes currently used. Two new methods of removing the silica template are reported, either by dissolving the silica in methanolic base or by dissolution in aqueous base under an external potential. The utility of these methods is demonstrated in the synthesis of hierarchically porous zinc oxide, nickel oxide, and copper monoliths that would dissolve or react using other template removal methods. The successful etching of monolithic zinc oxide using methanolic base etching can be explained by the reduced solubility of zinc oxide in methanol compared with an aqueous base, while it also reduces the formation of hydroxides when etching the nickel oxide and copper monoliths. Alternatively, the formation of highly soluble copper oxide/hydroxide can be avoided by holding the copper monolith at a sufficiently negative potential while etching with an aqueous base.

Among the different porous materials, bulk metallic glass (BMG) foams are of special interest due to their high strength combined with large elastic limit. Large surface areas and, therefore, high reactivity in chemical applications can be achieved by properly adjusting the pore characteristics. Pore size and pore size distribution are the key factors for determining the overall performance of open-cell porous materials used for functional applications, such as filtration or catalysis. As a result, the control of these factors is a necessary requirement for material design and application. In this work, BMG foams are produced by powder metallurgy through the selective dissolution of a fugitive phase. The work is focused on the manufacturing processes needed to properly control pore size and pore size distribution. The results reveal that customized hybrid BMG porous structures can be produced through the controlled milling of the BMG-composite powders.

Designing structures that have minimal or zero coefficients of thermal expansion (CTE) are useful in many engineering applications. Zero thermal expansion is achievable with the design of porous materials. The behavior is primarily stretch-dominated, resulting in favorable stiffness. Two and three-dimensional lattices are designed using ribs consisting of straight tubes containing two nested shells of differing materials. Differential Poisson contraction counteracts thermal elongation. Tubular ribs provide superior buckling strength. Zero expansion is achieved using positive expansion isotropic materials provided axial deformation is decoupled by lubrication or segmentation. Anisotropic materials allow more design freedom. Properties of two-dimensional zero expansion lattices, of several designs, are compared with those of triangular and hexagonal honeycomb nonzero expansion lattices in a modulus-density map. A three-dimensional, zero expansion, octet-truss lattice is also analyzed. Analysis of relative density, mechanical stiffness, and Euler buckling strength reveals high stiffness in stretch-dominated lattices and enhanced strength due to tubular ribs.

In this study, a powder blend representing 6061 Al-alloy was first mixed with Al2O3 ceramic particles and then foamed by using the powder compact melting method. 6061-Al2O3 foams and control specimens 6061 foams (without ceramic reinforcement) were produced. The effects of both different ratios of Al2O3 particle addition and different kinds of heat treatment on hardenability, structure and mechanical behavior of the final foams were investigated. Foams that were fully heat treated had the highest hardness values, and they performed best with an increase in collapse strength up to 100% over the untreated samples. Improved cell structure and decreased drainage were obtained when the Al2O3 addition was not more than 5 vol%. The compression test results were interpreted in terms of the foam’s microstructure, and correlations were made relating to the unloading modulus and compression strength of the foams to the relative density.

Ti-6Al-4V alloy with attractive properties such as corrosion resistance and high specific strength has a broad impact on daily life in the field of aerospace and medicine. The addition of TiC to Ti-6Al-4V is to further improve abrasion resistance and hardness. To have a low processing cost and precise control of the TiC volume fraction and distribution, the composite is densified with a blend of Ti-6Al-4V and TiC powders through a powder metallurgy route. The densification kinetics of the blend is studied for uniaxial die pressing (i) under isothermal conditions at 1020 °C, where β-Ti-6Al-4V deforms by creep and (ii) upon thermal cycling from 860 to 1020 °C, where the α-β transformation leads to transformation superplasticity. Densification curves for both isothermal and thermal cycling for various applied stresses and TiC fractions are in general agreement with predictions from continuum models and finite element simulation models performed at the powder level.

LM13 Al-alloy—cenosphere hybrid foam (HF) was made by foaming LM13 alloy–cenosphere mixture through a stir casting technique using CaCO3 as a foaming agent. In the melt mixture, 35 vol% of cenosphere was used and the foaming temperature was varied (660 and 690 °C). The foam contains microporosities as well as macroporosities and hence these are referred as HFs. The age-hardening characteristics and thereof deformation behavior of these foams have been examined using both microhardness and plateau stress measurements. It is further noted that energy absorption and plateau stress are maximum, and densification strain is minimum under peak-aged condition irrespective of the density of HF. Empirical relations are proposed to predict plateau stress, densification strain, and energy absorption as a function of aging time and relative density.

The development of porous metals has led to the need for an accurate prediction of the physical and mechanical properties of the many possible fabricated structures. For applications where yield stress needs to be reduced, while maintaining a high conductivity, the optimization of the pore dimensions, volume fraction, and pore spacing is required. A finite element model has been developed to simulate the effects of these factors on the electromechanical behavior of porous copper. This model was validated against samples of copper with mechanically induced pores as well as a copper GASAR sample. Good agreement (within an error of ±3%) was shown between the model and experimental data for the resistivity and effective modulus for both the mechanically induced pore and the GASAR samples, although the low ductility of the samples was not predicted and restricts the application of the simulation.

Heat transfer coefficients of porous copper samples with single- and double-layer structures, fabricated by the lost carbonate sintering process, were measured under forced convection conditions using water as the coolant. Compared with the empty channel, introducing a porous copper sample enhanced the heat transfer coefficient 5–8 times. The porous copper samples with double layers of porosities of 60% and 80% often had lower heat transfer coefficients than their single layer counterparts with the same overall porosities because the coolant flowed predominantly through the high-porosity layer. For the same double-layer structure, the order of the double layer had a large effect on the heat transfer coefficient. Placing the high-porosity layer next to the heat source was more efficient than the other way around. The predictions of a segment model developed for the heat transfer coefficient of multilayer structures agreed well with the experimental results.