Imre Norbert Orbulov

Infiltration Characteristics of Carbon Fiber Reinforced MMCs

Carbon fiber reinforced aluminum matrix composite blocks and a pipe (as semi-product) were produced by pressure infiltration technique. In this paper the authors deal with the production method and investigations of the blocks and the pipe. In our composites AlSi12 eutectic aluminium-silicon alloy was used as matrix material. The reinforcements were ‘A’ and ‘B’ type carbon fibers (‘A’ having lower amorphous carbon content than ‘B’). The volume fraction of the fibers was outstanding – at least 55 vol%. Scanning electron microscopic investigations were done in order to observe the rather rough surface of the carbon fibres. X-ray diffraction and energy dispersive spectrometry was done in order to estimate the quantity of Al4C3 intermetallic phase at the carbon fiber/matrix interface region. The measurements showed that the quantity of Al4C3 strongly depends on the amorphous carbon quantity in carbon fibers. Much more Al4C3 was formed in the case of ‘A’ type reinforcement (less amorphous carbon), than in the case of ‘B’ type reinforcement (more amorphous carbon). The presence of Al4C3 crystals caused large scatter in the mechanical properties, the UTS was decreased, while the compressive strength was increased. Fracture surfaces were investigated: the composite showed rigid fracture.

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.

Mechanical Behaviour Al-Matrix Composite Wires in Double Composite Structures

The fibre reinforced metal matrix composites (FRMMC-s) are one of the main groups of the composite materials. The composite wires are continuous-fibre-reinforced aluminium matrix composites, which are made by a continuous process. Composite wires already have a few experimental applications for the reinforcement of high voltage electric cables. Other experimental application fields of these materials are the preferential reinforcement of the cast parts. In this way significant decrease in the weight could be achieved. The aim of this study is to show the excellent mechanical properties of the composite wires, and the contact relationship between the mechanical and other properties (i.e. thermoelectric power) and the possibility of their standardized production. The continuous production process of the composite wires and their test results were are shown as well. The difference between the composite wire reinforced double composite structures and direct fibre reinforced blocks were delineated as well. In this paper specimens were examined by tensile tests, bending tests, thermal aging tests and thermoelectric power measurement.

Compressive Behavior and Microstructural Characteristics of Iron Hollow Sphere Filled Aluminum Matrix Syntactic Foams

Iron hollow sphere filled aluminum matrix syntactic foams (AMSFs) were produced by low pressure, inert gas assisted infiltration. The microstructure of the produced AMSFs was investigated by light and electron microscopy, extended by energy dispersive X-ray spectroscopy and electron back-scattered diffraction. The investigations revealed almost perfect infiltration and a slight gradient in the grain size of the matrix. A very thin interface layer that ensures good bonding between the hollow spheres and the matrix was also observed. Compression tests were performed on cylindrical specimens to explore the characteristic mechanical properties of the AMSFs. Compared to other (conventional) metallic foams, the investigated AMSFs proved to have outstanding mechanical properties (yield strength, plateau strength, etc.) and energy absorbing capability.

Microstructural aspects of ceramic hollow microspheres reinforced metal matrix composites

Abstract Ceramic hollow microsphere reinforced metal matrix syntactic foams were produced by means of pressure infiltration. The reinforcing ceramic hollow microspheres (SL300) microstructure was investigated. The microspheres contained various oxide ceramics, mainly Al2O3 and SiO2. The samples were characterized using X-ray diffraction measurements and energy dispersive spectroscopy maps. The results showed that the Al2O3 and SiO2 distribution in the wall of the microspheres is not equal; Al2O3 needles are embedded in the surrounding mullite and SiO2 phase. Line energy dispersive X-ray spectroscopy measurements showed that, due to the above mentioned uneven distribution of Al2O3 rich particles, a chemical exchange reaction took place between the aluminium alloy matrix and the microspheres and because of that the wall of the hollow microspheres became damaged.

Compressive strength and hardness of metal matrix syntactic foams

Six types of metal matrix syntactic foams (MMSFs) were produced by pressure infiltration technique. The foams were investigated by upsetting tests at increased (220°C) and at room (25°C) temperature. The parameters were the constituents of the composites and the aspect ratio (height-diameter ratio, H/D) of the specimens. The characteristic properties were: the compressive strength, the fracture strain, the structural stiffness of the foams and the absorbed energy. The strength, the strain and the energy were decreased while the stiffness was increased by increasing the H/D. Increased temperature caused ~25 % drop in the strength and in the stiffness. Macrohardness, depth sensitive and dynamic hardness tests were also performed on MMSF blocks: macrohardness is a structural property and independent from the matrix material. The depth sensitive hardness is sensitive to the deformation capability of the matrix and to a possible change reaction. The dynamic hardnesses of the MMSFs were higher than the hardness of the matrices and this is a microballoon related property.

Fatigue properties of expanded perlite/aluminum syntactic foams:

The main purpose of this paper is to present the basic fatigue properties of metal matrix syntactic foams. The investigated syntactic foams consisting of expanded perlite and A356 aluminum matrix were produced using an inert gas pressure infiltration technique. The obtained foams were subjected to cyclic compressive loading in order to investigate their fatigue properties. The standard procedure for cyclic fatigue testing was slightly modified to account for the variation of porosity and strength which is typical for metallic foam samples. This approach allows the direct comparison of the fatigue test results between all investigated samples. Depending on the applied load level, two different failure mechanisms were identified that resulted in characteristic deformation – loading cycle curves. The failure mechanisms were further investigated on the microstructural scale: traces of fatigue beachmarks and extensive plastic deformation were found. Furthermore, Wöhler-like deformation – lifetime diagrams were created in order to predict the expected lifetime of the properties of metal matrix syntactic foams .

Infiltration Characteristics and Compressive Behaviour of Metal Matrix Syntactic Foams

The most promising process for metal matrix syntactic foam (MMSF) production is pressure infiltration. In case if it can be advanced to die casting the cost of the MMSFs will drop significantly. The first step on this road is to characterize the kinetics of the pressure infiltration with respect to infiltration pressure and time. Experimental infiltration equipment was built and many preliminary tests were performed on the AlSi12 + SLG system. The load bearing capacity is also important, therefore the compressive behaviour of MMSFs were investigated. According to the results engineering factors (matrix material, size of the microballoons, applied heat treatment, temperature of the tests) have significant effects on the compressive properties.

On the effective Young’s modulus of metal matrix syntactic foams

ABSTRACT The effective Young’s modulus of aluminium matrix syntactic foams was determined by modal analysis. Two different matrix materials (Al99.5 and AlSi12) were used, and they were reinforced by Globocer grade ceramic hollow spheres. In order to validate the results, a full-scale finite element model was also created. A new algorithm was developed to place the spheres in a proper, probabilistic spatial distribution. Finite element simulations were carried out in modal analysis and compression test senses. In addition, three different analytical methods were studied to estimate the effective Young’s modulus. The measured values were compared with the finite element and analytical results. The determined effective Young’s moduli showed good agreement. This paper is part of a thematic issue on Light Alloys.

Global Approach of Tribomechanical Development of Hybrid Aluminium Matrix Syntactic Foams

Hybrid syntactic foams with AlSi12 aluminium matrix were produced by pressure infiltration. The volume ratio of iron to ceramic hollow sphere reinforcement (in the same size range) was varied, and hybrid syntactic foams were also produced with bimodal size ceramic reinforcement. Previously, a very detailed analysis of the mechanical properties of the composites was made with quasi-static compression tests, and their tribological properties were investigated by pin-on-disc method in dry and lubricated conditions. The present article establishes and clarifies the correlations between mechanical and tribological properties. The coefficient of friction, height loss of the specimens and specific wear showed good correlation with different mechanical parameters, e.g. density, structural stiffness and yield strength. The established trends and correlations between mechanical and tribological behaviour enable a better understanding of materials design and selection for further applications of mechanically loaded sliding machine parts.