Manas Mukherjee

The present work is the first ever study where the influence of beryllium (Be) addition on the stability of Mg alloy foam was investigated. Mg-3Ca alloy foams were produced by the liquid processing route with and without Be micro-addition. CaCO3 was used as a blowing agent. Mg-3Ca alloy foam without Be resulted in stable foam but exhibited low expansion with poor foam structure. Be addition significantly increased foam expansion and improved their structure. The expansion and the structure of the Mg foams obtained are comparable with that of commercially available aluminum foams. The XPS analysis confirmed the presence of BeO at the gas–solid interface of Mg foam. Be stabilizes the gas–solid interface of the foam by forming a smooth and crack-free surface of BeO layer which prevents the continuous oxidation of liquid foam and also minimizes the loss of blowing gas thereby enhancing the stability of Mg-3Ca alloy foams.

Abstract: In this study, the effectiveness of three different types of Mg-based blowing agents on the structure and properties of aluminum alloy foam was compared. AlMg15Cu10 alloy foams were produced by the powder metallurgy route using pure Mg, Al50Mg50 and Al60Mg40 powders as blowing agents. Al50Mg50 and Al60Mg40 powders were synthesized by ball milling and melt milling, and were characterized by particle size analysis, XRD and SEM. Foams were characterized by using X-ray tomography, SEM and XRD. Mechanical properties were obtained through quasi-static compression tests. It was observed that the foams produced by Mg possess spherical cells whereas more polyhedral cells were obtained in the foams produced by Al50Mg50 and Al60Mg40. The finest cells were produced by Al60Mg40 powder. Variation in the cell size is attributed to the different hydrogen contents of these blowing agents. All foams resulted in a good porous structure and possess high compressive strength compared with conventional foams. Graphical Abstract: [Figure not available: see fulltext.]

A novel method to produce foams from metallic melts was invented. It is referred here as melt injection method. An apparatus to produce foams by melt injection method was also developed. In this method, bubbles are created through air entrainment by injecting a jet of molten metal into a pool of molten metal. These bubbles rise to the surface of melt pool and create a foam there. This method works without the need of an additional processing step to produce or add stabilising particles in the melt. In this study, foam from pure Al melt was produced with 93% porosity. X-ray tomography was used to visualise the macrostructure of the foams. Microstructural and phase analysis were carried out using SEM and XRD, respectively. These studies revealed the formation of alumina layer and particles at the gas-solid interface of cell walls. Stabilisation of foams produced by melt injection method was attributed to the combined action of oxide layer and particles. The mechanism of bubble formation through air entrainment was studied by using a water model set up.

Abstract: Aluminium and Al-TiB2 closed-cell foams were produced by a recently developed foaming method called melt injection technique where bubbles are created by air entrainment. The macro- and microstructures of the foams were characterised by X-ray tomography and scanning electron microscopy, respectively. Mechanical properties were evaluated by quasi-static compression tests. Al-TiB2 foam exhibited finer cells and better mechanical properties compared to Al foam. Also, the structural and mechanical properties of these foams were compared with closed-cell foams produced by other existing methods. Graphic abstract: [Figure not available: see fulltext.].

In this article, we demonstrate a technique to visualise the stabilising particles at the gas-solid interface of metal foams by employing metallographic etching. This technique is easy to perform and can be applied on a relatively large sample size. The particles present at the gas-solid interface of five different types of foams were investigated. Information on the type of particles and the particle coverage could be obtained from this study.

In this work, we present a simple and scalable approach for fabricating porous ceramic from emulsions stabilized by a binary mixture of oppositely charged nanoparticles and a polyelectrolyte. The electrostatic heteroaggregation is exploited to form weakly charged particle–polyelectrolyte complexes (PPCs) that readily stabilize oil-in-water emulsions. The concentration of surface-active PPCs is varied to obtain Pickering emulsion gels that can be processed and converted into the macroporous ceramic structure. The polyelectrolyte in the binary mixture not only enables the adsorption of particles to the oil–water interface and renders processability of the emulsions but also acts as a binder. Nearly one-to-one correspondence between the microstructure of the green ceramic obtained after the evaporation of solvents from the gel-like emulsions and the parent emulsions is observed. The green ceramic is further sintered under controlled conditions to obtain a porous ceramic monolith. We demonstrate that the microstructure and the pore size distribution in the final ceramic can be altered by tuning the composition of the individual species used in the emulsion formulation, i.e., by optimization of the particle–polyelectrolyte ratio used in the processing route.

The requirement for an alloy-specific heat treatment of TiH2 for producing foams by the powder metallurgy route was demonstrated in this study. Three heat-treated TiH2 powders were used to produce foams from three Al–Si–Mg alloys having different liquidus temperatures. Dehydrogenation behaviour of heat-treated TiH2 was studied using mass spectroscopy and thermogravimetry analysis. Foams were characterised by means of X-ray tomography. Quasi-static compression tests were employed to test their mechanical property. Using a combination of three alloys and three heat treatments, it was demonstrated that a good foam structure can be obtained when the maximum hydrogen release from TiH2 takes place after the complete melting of the alloy. The amount of hydrogen released during solid and semisolid stages of foaming also play a role in determining the final structure of the foams. It was also observed that such foams with a good structure possess a higher strength compared to the foams produced by using blowing agent that releases maximum hydrogen before complete melting.

In this study, it was shown that aluminum powder can be used as stabilizing particles for the fabrication of aluminum foams by melt route. When Al powder was mixed with the TiH2 before adding into the melt, it also acted as dispersing agent for the TiH2 thus further improving the structure of the foams. Stirring during powder mixing also contributed towards foam stability by introducing oxides into the melt. The oxides were examined using SEM/EDS and oxygen analyzer.

Monitoring foam expansion and the study of foaming kinetics during in-situ foam filling are essential to ensure a desirable quality of foam-filled profiles. In this current research, a novel technique is proposed for monitoring in-situ aluminum foam filling of hollow profiles. In this technique, instantaneous temperatures measured at various locations of the hollow profile being filled have been used to determine the foam expansion rate. Hence, the apparatus developed in this study is named as thermal expandometer. To demonstrate the usefulness of this thermal expandometer, aluminum foaming is performed inside a steel tube by heating the foaming precursor at different rates, and an analysis of the effect of heating rate on the foam expansion rate is presented.

The main focus of the present study is to compare the effect of different alloying elements on Al–Mg alloy foams. Al–Mg15–X10 (X = Cu, Zn and Si) alloy foams were produced via powder metallurgy route by using Mg as a blowing agent. Macro- and microstructural characterisations of the foams were performed using X-ray tomography, X-ray diffraction and scanning electron microscope. Corrosion studies such as weight loss measurement, hydrogen evolution method and potentiodynamic test were conducted. Mechanical properties were evaluated by subjecting the samples to quasi-static compression and microhardness tests. All the alloy foams showed a comparable structure. The Cu-containing foams exhibited the highest strength, while the Zn-containing foams showed the highest expansion. However, the other properties such as brittleness, elastic modulus and burning nature were found to be better for the Si-containing foams.