Development and evaluation of hybrid aluminium matrix syntactic foams

A special class of metallic foams, the so called metal matrix syntactic foams was produced by pressure infiltration technique. Metal matrix syntactic foams consist of a light-weight metal matrix and a set of hollow spheres. Microstructural investigatons were done on polished specimens. The results showed almost perfect infiltration and thin interface layer between the matrix and the reinforcement. Quasi-static compression tests were also done to get basic information about the mechanical properties of metal matrix syntactic foam. The results showed outstanding mechanical properties among other metallic foams. The tests were performed in order to prepare pin-on-disc wear tests

Microstructure of metal matrix composites reinforced by ceramic microballoons

Metal matrix composites reinforced by ceramic hollow microspheres were produced as special porous metals, called metal matrix syntactic foams (MMSFs). In this paper the microstructure of the ceramic hollow microspheres as reinforcing element was investigated in connection with the production of MMSFs by pressure infiltration. SL150 and SL300 type ceramic microspheres from Envirospheres Ltd. (Australia) were investigated. They contained various oxide ceramics, mainly Al2O3 and SiO2. The chemical composition and the microstructure of the microspheres had strong effect on their infiltration characteristics; therefore in the view of MMSF production it was very important to know microstructural details about the microspheres. Due to this energy dispersive X-ray spectroscopy maps were recorded from the cross 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. Line energy dispersive X-ray spectroscopy measurements were performed in order to investigate the possible reaction between the different aluminium alloy matrices and the ceramic microspheres. The results showed that, due to the uneven distribution of Al2O3 rich particles, the molten aluminium could reduce the SiO2 rich parts of the microspheres and the wall of the hollow microspheres became damaged and degraded. This chemical reaction between the microspheres and the walls could make the infiltration easier, but the resulting mechanical properties will be lower due to the damaged microsphere walls

Syntactic foams produced by pressure infiltration - the effect of pressure and time on infiltration length

Ceramic hollow microballoons were incorporated into aluminium matrix to produce metal matrix syntactic foams (MMSFs). Syntactic foams have low density and relatively high strength; therefore they can be used as materials of many important parts in automotive technology or in aviation and sea industry. The MMSFs can be produced by pressure infiltration technique, which can be productive if it is modified in the direction of injection casting. The aim of this paper is to determine the necessary pressure and time parameters for the successful infiltration of a given length. A measurement system was developed and applied to investigate the effect of pressure and time on infiltrated length. In this paper the results of these preliminary measurements are presented. Power law ruled surface was fitted on the measured points in order to evaluate the infiltrated length for any pressure and time parameters. The results were compared to the theoretically predicted ones and on this base an advanced measurement system is s uggested and designed

Compressive behaviour of metal matrix syntactic foams

The compressive behaviour of three different metal matrix syntactic foams (MMSFs) were investigated. The results showed that the engineering factors as the size of the used hollow spheres, the aspect ratio (height / diameter ratio) of the specimens and the temperature of the compression tests have significant effects on the compressive strength and properties. The smaller microballoons with thinner wall ensured higher compressive strength due to their more flawless microstructure and better mechanical stability. The higher aspect ratio of the specimens resulted in worse compressive characteristics (lower strength, lower specific energy consuming capacity). The elevated temperature tests revealed ~30% drop in the compressive strength. However, the strength remained high enough for structural applications; therefore MMSFs are good choices for light structural parts working at elevated or room temperature. The proper size selection of the reinforcing hollow spheres ensures potential for tailoring the compressive characteristics of MMSFs

XRD and EDS Investigations of Metal Matrix Composites and Syntactic Foams

Metal matrix composites (MMCs) of different composition were produced and investigated by X-ray diffraction (XRD) and energy dispersive spectrometry (EDS) analysis. Firstly unidirectionally reinforced MMCs were produced using two type carbon fibre reinforcement and commercial purity aluminium matrix. In MMCs the interface layer has significant effect on the mechanical properties of the composites therefore need to be correctly explored. The investigations showed chemical composition changes in the composites, especially at the interface layers. In the case of carbon fibre reinforced composites Al4C3 phase was formed. The amount of Al4C3 depended on the temperature and the time at temperature of the composite during production and on the quality of carbon fibres. As the second investigated MMC, SiC fibre reinforced aluminium matrix composite wires were produced by continuous pressure infiltration. In SiC reinforced MMC wires the effect of interface diffusion was observed. After long term thermal ageing at 300°C alumina was formed and Si and Ti of SiC fibres moved into the matrix. Finally, metal matrix syntactic foams were manufactured which are particle-reinforced composites, but also known as porous materials (foams), because they contain high amount of hollow ceramic microspheres. Four type hollow spheres from different suppliers with different chemical composition and mean diameters were used. In syntactic foams an exchange reaction took place between the aluminium alloy matrix and the Si content of ceramic inclusions. The reaction resulted in significant alumina formation

The processing and testing of aluminium matrix composite wires, double composites and block composites

The Composite Processing and Testing Laboratory operated for about 15 years in USA. After that, in 2004- 2005, it moved from Boston to the Budapest University of Technology and Economics One of the main results from research and development projects is that of aluminium matrix composite wires produced via continuous processing. The composite wires have experimental applications for the electrically conductive reinforcement of high voltage electric cables, for example. Ceramic continuous-fibre-reinforced MMC-wires were produced with diameters ranging from 0.1 to 2.5 mm and a fibre volume fraction of up to 60% v/o. Thanks to the high efficiency of the continuous process, interface relations are notably reduced, and this increases mechanical properties. The other principal result is one pointing to carbon fibre-reinforced block composites processed by a combination of vacuum and high-pressure infiltration. The result of these processes is fibre-reinforced aluminium matrix composite blocks. Production methods, composite wire reinforced double composites and the results of the material tests of these products are revealed. Various matrixes were made use of in the production of double composites so as to monitor the changes in the interface relations. Alongside the conventional mechanical testing methods, mechanical properties can be characterized by use of an instrumented impact test, while the solidification structure and interfacial properties can have a SEMEDS and thermoelectric measurement (Seebeck-coefficient)

Composite production by pressure infiltration

This paper presents the possibility of composite block production by using pressure infiltration technology. This method uses the pressure of an inert gas (usually argon or nitrogen) to force the melted matrix material to infiltrate the reinforcing elements. Three types of materials were considered: open cell metallic foam, metal matrix syntactic foam and carbon fiber reinforced metal matrix composite. Physical and mechanical investigations – such as SEM and compression tests – were performed. The results of measurements were summarized briefly

Manufacturing of Composites by Pressure Infiltration, Structure and Mechanical Properties

This paper presents the possibility of composite block production by using pressure infiltration technology. This method uses the pressure of an inert gas (usually argon or nitrogen) to force the melted matrix material to infiltrate the reinforcing elements. Two types of materials were considered: metal matrix syntactic foam and carbon fibre reinforced metal matrix composite. Physical and mechanical investigations – such as optical microscopy, scanning electron microscopy (SEM), X-ray diffractography (XRD), tensile and upsetting tests (considering aspect ratio) – were performed. The results of measurements are summarized briefly here. Microscopic investigations showed almost perfect infiltration. XRD measurements and tensile tests revealed negative effect of an intermetallic phase (Al(4)C(3)) on ultimate tensile strength (UTS). Syntactic foams showed plateau region in their upsetting diagrams. The effect of aspect ratio was also investigated. Specimens with higher aspect ratios showed higher peak stress and higher modulus of elasticity. In the case of carbon fibre reinforced metal matrix composites Al(4)C(3) ensured high compressive fracture strength

Characterisation of hybrid metal matrix syntactic foams

High quality aluminium matrix syntactic foams (AMSFs) were produced by pressure infiltration. This method can ensure the maximal volume fraction of the reinforcing hollow spheres and very low amount of unwanted or matrix porosities. By this method hybrid MMSFs with mixed metal and ceramic hollow spheres were also produced. The matrix material was AlSi12 alloy and two different types – produced by Hollomet GmbH in Germany – of hollow spheres were used: Globomet (GM) and Globocer (GC). The geometrical properties of the hollow spheres were similar (average outer diameter), but their base material was pure iron and Al2O3+SiO2 in the case of GM and GC hollow spheres respectively. The volume fraction of the reinforcing hollow spheres were maintained at ~65 vol%, but the ratio of them was altered in 20% steps (100% GM + 0% GC, 80% GM + 20% GC…). The results of the compression tests showed, that the compressive strength, yield strength, plateau strength, structural stiffness and the absorbed mechanical energy values increased with higher ceramic hollow sphere reinforcement ratio. The fracture strains of the investigated MMSFs decreased with the higher GC ratio. Generally the strength values also increased with higher diameter to height (H/D) ratio from H/D=1 to H/D=1.5 and 2