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Journal ArticleDOI

On the microstructure of ceramic hollow microspheres

TL;DR: In this paper, the microstructure of the ceramic hollow microspheres as reinforcing element was investigated, and the results showed that the Al2O3 and SiO2 distribution was not equal; the Al 2O3 phase was embedded in the surrounding mullite and Si O2 phase in the form of needles.
Abstract: Metal matrix syntactic foams (MMSFs) are relatively new materials which have increasing interest in the field of aviation and packaging industry. They are metal matrix composites, and their porosity is ensured by the incorporation of ceramic hollow microspheres. In this paper the microstructure of the ceramic hollow microspheres as reinforcing element was investigated. SL150, SLG and SL300 type ceramic microspheres were investigated. They contain various oxides, mainly Al2O2 and SiO2. Energy dispersive X-ray spectroscopy (EDS) maps were recorded from the sections of the microspheres’ wall. The results showed that the Al2O3 and SiO2 distribution was not equal; the Al2O3 phase was embedded in the surrounding mullite and SiO2 phase in the form of needles. EDS along a line in aluminium matrix syntactic foams was carried out in order to investigate the possible reaction between the aluminium matrix and the ceramic microspheres. Due to the uneven distribution of Al2O3 rich particles, the molten aluminium can reduce the SiO2 rich parts of the microspheres and the wall of the microspheres become damaged and degraded. This chemical reaction between the microspheres and the walls can make the infiltration easier, but the resulting mechanical properties will be lower due to the damaged microsphere walls.

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TL;DR: In this paper, an AlSi12 matrix hybrid MMSF with monomodal Globocer (Al 2 O 3 and SiO 2 based ceramic) and pure Fe reinforcements were produced by pressure infiltration.
Abstract: Hybrid metal matrix syntactic foams (hybrid MMSFs) are particle reinforced composites in which the reinforcement is the combination of more than one grade of hollow spheres. The difference between the spheres can be in their chemical composition, dimension, physical properties etc. In this study AlSi12 matrix hybrid MMSFs with monomodal Globocer (Al 2 O 3 and SiO 2 based ceramic) and Globomet (pure Fe) reinforcements were produced by pressure infiltration. The investigation parameters were the ratio of the hollow sphere grades and the aspect ratio of the specimens. Microstructural investigations showed almost perfect infiltration and favourable interface layer, while quasi-static compression tests showed that the composition of the reinforcement and the aspect ratio of the specimens have determinative effect on the characteristic properties (compressive and flow strength, fracture strain, stiffness and absorbed energy). This nature of the MMSFs ensures the possibility to tailor their properties in order to optimise them for a given application.

65 citations

Journal ArticleDOI
TL;DR: In this article, metal matrix syntactic foams (MMSFs) were produced by pressure infiltration and two parameters of the infiltration process (pressure and time) were varied and the infiltrated length was measured as the function of infiltration parameters in order to get data for the implementation of pressure infiltration as mass-production of MMSFs similar to injection mould casting, especially in the short infiltration time range.
Abstract: Metal matrix syntactic foams (MMSFs) were produced by pressure infiltration. Two parameters of the infiltration process (pressure and time) were varied and the infiltrated length was measured as the function of infiltration parameters in order to get data for the implementation of pressure infiltration as mass-production of MMSFs similar to injection mould casting, especially in the short infiltration time range (

64 citations

Journal ArticleDOI
TL;DR: In this article, aluminum alloy matrix syntactic foams were produced by inert gas pressure infiltration and four different alloys and ceramic hollow spheres were applied as matrix and filler material, respectively, the effects of the chemical composition of the matrix and the different heat-treatments are reported at different strain rates and in compressive loadings.
Abstract: Aluminum alloy matrix syntactic foams were produced by inert gas pressure infiltration. Four different alloys and ceramic hollow spheres were applied as matrix and filler material, respectively. The effects of the chemical composition of the matrix and the different heat-treatments are reported at different strain-rates and in compressive loadings. The higher strain rates were performed in a Split-Hopkinson pressure bar system. The results show that, the characteristic properties of the materials strongly depends on the chemical composition of the matrix and its heat-treatment condition. The compressive strength of the investigated foams showed a limited sensitivity to the strain rate, its effect was more pronounced in the case of the structural stiffness and fracture strain. The failure modes of the foams have explicit differences showing barreling and shearing in the case of quasi-static and high strain rate compression respectively.

55 citations


Cites methods from "On the microstructure of ceramic ho..."

  • ...9 grinded on an automatic grinding and polishing machine with SiC papers and diamond suspension, respectively [52-54]....

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Journal ArticleDOI
TL;DR: In this paper, the in situ reaction between silica (phase of mullite) and aluminium particles, apart from any degradation of the mullite cell wall and the precipitation of silicon in the matrix, changes the sintering mechanism of syntactic foams due to the formation of eutectic aluminium-silica liquid quantities.
Abstract: Metal matrix syntactic foams of ceramic (mullite) cenospheres (10–40% v/v) embedded in pure aluminium matrix, were fabricated by powder metallurgy technique at different sintering temperatures (610–710 °C). Density, vis-a-vis porosity and microstructural characteristics were examined by using scanning electron microcopy and energy dispersive X-ray spectroscopy. A first systematic description of the sintering mechanism of the composites is presented. The in situ reaction between silica (phase of mullite) and aluminium particles, apart from any degradation of the mullite cell wall and the precipitation of silicon in the matrix, changes the sintering mechanism of syntactic foams due to the formation of eutectic aluminium–silica liquid quantities. Transient liquid phase sintering, with surface material diffusion, and liquid phase sintering, with bulk diffusion, selected to be the main sintering mechanisms, are described in detail for sintering temperatures below and above the melting point of aluminium matrix, respectively.

41 citations

Journal ArticleDOI
TL;DR: In this article, the effects of specimen aspect ratio (the thickness/width ratio, AR) on the compressive properties of closed-cell Mg alloy foams were investigated systematically and the results showed that the length of stress strain plateau stage extended and ideality energy absorption efficiency improved with the specimen AR increasing and the yield strength decreased.

27 citations

References
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Journal ArticleDOI
TL;DR: In this article, hollow fly ash particles (cenospheres) were pressure infiltrated with A356 alloy melt to fabricate metal-matrix syntactic foam, using applied pressure up to 275kPa.
Abstract: Loose beds of hollow fly ash particles (cenospheres) were pressure infiltrated with A356 alloy melt to fabricate metal-matrix syntactic foam, using applied pressure up to 275 kPa. The volume fractions of cenospheres in the composites were in the range of 20–65%. The processing variables included melt temperature, gas pressure and particles size of fly ash. The effect of these processing variables on the microstructure and compressive properties of the synthesized composites is characterized. Compressive tests performed on these metal-matrix composites containing different volume fractions of hollow fly ash particles showed that their yield stress, Young's modulus, and plateau stress increase with an increase in the density. Variations in the compressive properties of the composites in the present study were compared with other foam materials.

258 citations

Journal ArticleDOI
TL;DR: In this paper, synthetic foams were fabricated by liquid metal infiltration of commercially pure and 7075 aluminum into preforms of hollow ceramic microspheres, which exhibited peak strength during quasi-static compression ranging from −100 to −230 MPa, while dynamic compression loading showed a 10-30% increase in peak strength magnitude, with strain rate sensitivities similar to those of aluminum-matrix composite materials.
Abstract: Syntactic foams were fabricated by liquid metal infiltration of commercially pure and 7075 aluminum into preforms of hollow ceramic microspheres. The foams exhibited peak strengths during quasi-static compression ranging from −100 to −230 MPa, while dynamic compression loading showed a 10–30% increase in peak strength magnitude, with strain rate sensitivities similar to those of aluminum–matrix composite materials. X-ray tomographic investigation of the post-compression loaded foam microstructures revealed sharp differences in deformation modes, with the unalloyed-Al foam failing initially by matrix deformation, while the alloy–matrix foams failed more abruptly through the formation of sharp crush bands oriented at about 45° to the compression axis. These foams displayed pronounced energy-absorbing capabilities, suggesting their potential use in packaging applications or for impact protection; proper tailoring of matrix and microsphere strengths would result in optimized syntactic foam properties.

212 citations

Journal ArticleDOI
10 May 2007-Wear
TL;DR: In this paper, the wear and friction characteristics of the composite in the as-cast conditions were studied by conducting sliding wear test, slurry erosive wear test and fog corrosion test.

210 citations

Journal ArticleDOI
TL;DR: In this paper, syntactic foams were fabricated by pressure-infiltrating liquid aluminum (commercial purity and 7075-Al) into a packed preform of silica-mullite hollow microspheres.

141 citations

Journal ArticleDOI
Gaohui Wu1, Zuoyong Dou1, D.L. Sun1, Longtao Jiang1, B.S. Ding1, B.F. He1 
TL;DR: In this article, a new method was established to predict the compressive strength of cenosphere-aluminum syntactic foams, showing the relation between the relative wall thickness of the cenopshere and the Compressive Strength of such foams.

140 citations