Pressure Infiltration Technique Research Articles

Melt infiltration of SiCp reinforced Al matrix composite by newly designed pressure infiltration technique

Newly designed pressure infiltration technique was developed to clarify the molten metal flow through solid network, aiming to obtain property materials and, simultaneously, the purified matrix as a filtrated metal. An experimental apparatus was constructed to control the microstructure morphology for varied fraction of solid and applied pressure. A sample, Al-7 wt.% Si-20 vol.% SiCp was squeezed on the double layers of semi-solid aluminum alloy cake and alumina porous medium by using argon gas pressure. Permeability values were estimated by Darcy's law in order to know the molten metal flow characteristics through solid network in the semi-solid range. It was found that the permeability suddenly decreased with increasing fraction of solid, and filtration mechanism was changed between depth and cake filtration near fraction of solid 0.25 due to much difference of the flow resistance between the two. Increasing applied pressure decreased the permeability due to the consolidation of solid grains. For pressurized sample on the filter and filtrated metal, SiCp content became to as high as 38 and less than 0.4 in volume percentage depending on fraction of solid, respectively. The pressurized samples with high SiCp content showed low wear rate and high hardness, when compared with original composite sample.

Thermal Expansion of Aluminum–Fly Ash Cenosphere Composites Synthesized by Pressure Infiltration Technique

The coefficients of thermal expansion (CTEs) of commercially available pure aluminum and aluminum alloy composites containing hollow fly ash particles (cenospheres) of average size 125 mm are measured using a dilatometer. Three types of composites are made using the pressure infiltration technique at applied pressures and infiltration times of 35 kPa for 3 min, 35 kPa for 7 min, and 62 kPa for 7 min. The volume fractions of the fly ash cenospheres in the composites are around 65%. The CTE of the composites is measured to be in the range of 13.1×10-6-11×10-6/°C, which is lower than that of pure aluminum (25.3×10-6/°C). The infiltration processing conditions are found to influence the CTE of the composites. A higher applied pressure and a longer infiltration time lead to a lower CTE. The theoretical value of the CTE of fly ash cenospheres is estimated to be 6.1×10-6/°C.

Compressive characteristics of A356/fly ash cenosphere composites synthesized by pressure infiltration technique

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.

Wear behaviour of Al/(Al 2O 3p+SiC p) hybrid composites

In this study, dry sliding metal–metal and metal–abrasive wear behaviours of the aluminium matrix hybrid composites produced by pressure infiltration technique were investigated. These composites were reinforced with 37 vol% Al 2O 3 and 25 vol% SiC particles and contained up to 8 wt% Mg in their matrixes. While matrix hardness and compression strength increased, amount of porosity and impact toughness decreased with increasing Mg content of the matrix. Metal–metal and metal–abrasive wear tests revealed that wear resistance of the composites increased with increasing Mg addition. On the other hand, abrasive resistance decreased with increasing test temperature, especially above 200 °C.

Properties of nanostructured diamond-silicon carbide composites sintered by high pressure infiltration technique

A high-pressure silicon infiltration technique was applied to sinter diamond–SiC composites with different diamond crystal sizes. Composite samples were sintered at pressure 8 GPa and temperature 2170 K. The structure of composites was studied by evaluating x-ray diffraction peak profiles using Fourier coefficients of ab initio theoretical size and strain profiles. The composite samples have pronounced nanocrystalline structure: the volume-weighted mean crystallite size is 41–106 nm for the diamond phase and 17–37 nm for the SiC phase. The decrease of diamond crystal size leads to increased dislocation density in the diamond phase, lowers average crystallite sizes in both phases, decreases composite hardness, and improves fracture toughness.

Effect of SiC particle size on corrosion behavior of pressure infiltrated Al matrix composites in a NaCl solution

In this study, the effect of SiC particle size on corrosion behavior of Al-60 vol.% SiC particle composites has been investigated. Three different SiC particle composites, having mean diameters of 13, 23 and 37 μm, were produced by a pressure infiltration technique at 750 °C. The corrosion tests were carried out in 3.5 wt.% NaCl environment up to 28 days. Experimental results showed that the weight loss of the composites increased with increasing particle size and exposure time. However, weight loss of the composites having 13- and 23-μm particle sizes remained almost constant after 3–5 days of exposure time. Scanning electron microscopic (SEM) analysis and potentiodynamic polarization measurements revealed that composite having 13-μm SiC particles exhibited higher corrosion resistance than that of the composites having 23- and 37-μm SiC particles. Experimental results showed that intermetallics as a result of reaction between Al and SiC particle has a beneficial effect on corrosion resistance of the composites due to interruption of the continuity of the matrix channels within the pressure infiltrated composites.

Mechanical properties of Al-60 Pct SiCp composites alloyed with Mg

In the present work, the effect of an Mg addition on the mechanical properties of the Al-60 vol pct SiCp composites were investigated by uniaxial compression, three-point bending, impact and wear tests (composite-metal and composite-abrasive types). The composites were produced by the pressure-infiltration technique. The composition of the Al matrix was varied between 0 and 8 pct Mg. The mean diameter of the SiC particles was 23 µm. Upon addition of Mg, Mg2Si precipitated in the matrix and the amount of the porosity dramatically decreased. Mg-alloyed-matrix composites exhibited higher strength, lower toughness, and higher wear resistance than pure-Al-matrix composites. During composite-metal wear testing, wear progressed in two sequential periods (running-in and steady state). Weight loss during wear testing decreased with increasing Mg content of the matrix. The degree of improvement of abrasive resistance depended on the abrasive-grain size. Above 200 °C, the composite-abrasive wear resistance decreased with increasing test temperature for all materials.

Corrosion behavior of Al–60 vol.% SiC p composites in NaCl solution

In this study, corrosion behavior of pure Al and Al–4 wt.% Mg alloy matrix composites, comprising 60 vol.% SiC particles, has been investigated. Composites were produced by pressure infiltration technique at 750 °C. The corrosion tests were carried out in 3.5 wt.% NaCl environment up to 28 days. The weight loss of the composites increased with increasing duration time up to 3–5 days then remained constant. Scanning electron microscopy (SEM) analysis showed that Al–4 wt.% Mg alloyed matrix composite exhibited higher corrosion resistance than pure Al matrix composite although potentiodynamic polarisation measurements showed higher i corr values of Al–4 wt.% Mg alloyed matrix composites than pure Al matrix composites. Experimental results revealed that precipitation of Mg 2Si as a result of reaction between Al–Mg alloy and SiC particle has a beneficial effect on corrosion resistance of Al–4Mg alloy matrix composites due to interruption of the continuity of the matrix channels within the pressure infiltrated composites.

Abrasive wear behavior and mechanical properties of Al–Si/SiC composites

In this study, the effect of Si addition up to 8% Si on the abrasive wear and mechanical properties of Al–Si/60 vol.% SiC composites produced by pressure infiltration technique has been investigated. Optimum properties in terms of improved strength and abrasion resistance without significant loss in toughness were obtained when the matrix alloy contained 1% Si. At Si contents higher than 1%, dramatic decrease of toughness was accompanied a reduction in strength and abrasion resistance.

Effect of the Particle Size on the Mechanical Properties of 60 Vol.% SiCpReinforced Al Matrix Composites

Abstract The effect of the reinforcing particle size on the mechanical properties of 60 vol.% SiC reinforced aluminium matrix composites produced by the pressure infiltration technique was examined by compression, impact and wear tests. The compression strength and the impact resistance decreased with increasing reinforcing particle size. The composites exhibited different abrasion behaviour depending on the size of abrasive Al2O3 grains. On fine abrasive Al2O3 grains (85 μm), the abrasion resistance increased with increasing reinforcing SiC particle size. The contrary result was obtained on coarse abrasive Al2O3 grains (250 μm). The wear tests conducted on M2 quality tool steel revealed that reinforcing of aluminium with coarse SiC particles has a very beneficial effect on the wear resistance with respect to fine reinforcing SiC particles.

Fabrication of high-temperature resistant oxide ceramic matrix composites

Abstract The main objectives of this work are to develop and apply new ceramic matrix materials by which a relatively high level of densification of the final composite may be achieved by pressureless-sintering at temperatures close to 1200°C. A cost-effective processing method for the production of oxide/oxide CMCs materials and components has been achieved. A range of interphase materials is applied to Nextel™ 720 fibres. These include zirconia, neodymium and lanthanum phosphate. A combination of ZrO 2 and the AKP50 alumina powder have been selected as the successful candidates for the interphase and the matrix material, respectively. Work has been conducted on the preparation of slurry systems consisting of these two materials. The prime target was to establish the possibility of achieving good coating around the bulk of the fibres together with a high level of impregnation with the matrix material. Furthermore, the pressure infiltration technique has been applied and as a result composite samples with fibre volume content of 40%, and remaining porosity of around 20 vol% have been routinely produced. Composite room and high-temperature tensile strengths of around 200 MPa have been accomplished.

Abrasive wear behaviour of Al–SiC composites produced by pressure infiltration technique

In this study, abrasive wear behaviours of compacts produced by pressure infiltration technique were investigated. Pure aluminium and SiC particles having 13 and 37 μm mean diameters were used in the infiltration process. The volume fraction of the SiC particles was 60% in the compacts. Abrasive wear tests were carried out under the normal load of 28 N, by rubbing the compacts to abrasive Al 2O 3 grains with diameters in the range of 85–250 μm. Wear tests revealed that, the effect of the size of SiC particles on the wear resistance of compacts, depends on the size of the Al 2O 3 abrasive grains being rubbed. The compact which had 13 μm SiC particles exhibited higher wear rate than the compact having 37 μm SiC particles when rubbed on fine abrasive Al 2O 3 grains (<150 μm). Wear tests performed on Al 2O 3 abrasive grains having diameters higher than 150 μm revealed that, the compact reinforced with 37 μm SiC particles had higher wear rate than the compact reinforced with 13 μm SiC particles.

Characterisation of anisotropic elastic constants of continuous alumina fibre reinforced aluminium matrix composite processed by medium pressure infiltration

The anisotropic elastic properties of an Al metal matrix composite unidirectionally reinforced with continuous α-alumina fibres fabricated, by a medium pressure infiltration technique, has been characterised using ultrasonic bulk and surface waves, tensile tests and microstructural analysis. The ultrasonic data are analysed under the continuum mechanics approximation. Elastic anisotropy is studied by varying the direction of propagation of ultrasonic waves. An optimisation process is used to recover all the volumic effective elastic moduli from bulk ultrasonic velocities. Two local (sub-surface) shear effective moduli are determined from the surface waves velocities. To discuss the elastic anisotropy of the material in relation with its microstructure and the manufacturing process, microstructural observations are correlated to the global and local ultrasonic evaluations and to the mechanical characterisation conducted in and out of symmetry axis.

Tri-dimensionally continuous network reinforced metal-matrix composite and its manufacturing method

A new type of tri-dimensionally continuous network reinforced metal-matrix composite was proposed and an effective manufacturing method was advanced. By employing the SHS reaction of AI-TiO2,-C system and vacuum high pressure infiltration technique, the making of this type of metal-matrix composite has been thoroughly studied. Emphasis was placed on the law of the formation of interconnected porous network structure in the SHS reaction products. By means of OM and SEM the obtained highly porous SHS reaction products and the resulting tridimensionally continuous network reinforced metal-matrix composite have been closely examined.

Fabrication Process for Continuous Magnesium/Carbon-Fibre Composites with Graded Fibre Content

A process has been developed which allows the adjustment of fibre volume fraction in a range from 30 to 60 vol.-% for unidirectionally long fibre reinforced metal matrix composites (MMCs). An impregnation method with a water-particle suspension is used to introduce ceramic particles as spacers in a carbon fibre roving. The amount of particles and the resulting fibre volume fraction can be varied by changing process, tooling and material parameters. The main parameters influencing the fibre volume fraction are the roving winding speed, the particle concentration and particle size. After fabrication the fibre preforms are infiltrated by a gas pressure infiltration technique with the magnesium alloy AM20 and characterised mechanically (Young modulus, tensile and bending strength) as well as physically (thermal expansion). In conclusion a locally fibre reinforced shaped part with a graded fibre content is presented.

Temperature dependent strength analysis of short fiber reinforced Al–Si metal matrix composites

Abstract Metal matrix composites (MMCs) were produced by a pressure infiltration technique, using Saffil ( δ -Al 2 O 3 ) alumina short fiber preforms as the reinforcement, and the alloy Al–12 wt% Si (LM 13) as the matrix material. The matrix alloy and the composites were subjected to a standard T6 heat treatment and consequently tensile tested. The room temperature strength of the composites were seen to increase up to 15 vol.% fiber and then deviated sharply from the linear behavior and decrease continuously as the fiber volume increased. As the test temperature was raised, all composites showed excellent retention of strength up to 300°C. Furthermore, the experimental results of tensile strength were compared to a modified rule of mixtures (ROM). The high temperature strength analysis showed that the strength of planar-randomly oriented short fiber reinforced material can be explained through combined effects of load transfer, dispersion strengthening, and dislocation strengthening. The reinforcement behavior of these type of composites is seen to be controlled by the elevated temperature properties of the matrix alloy. The theoretical tensile strength values, calculated with a temperature dependent modified rule of mixture equation, showed an excellent agreement with experimental data at room temperature and also at elevated temperatures of up to about 200°C.

Effect of Particle Additions on Drying Stresses and the Green Density of Sol‐Gel‐Processed Three‐Dimensional Ceramic‐Matrix Composites

This paper investigates sol‐gel processing of three‐dimensional (3‐D) ceramic‐matrix composites, focusing on the effect of addition of particles on drying stresses and composite green density. A 3‐D woven carbon fiber/silica composite was used as the model material system for the investigation. Composites were fabricated with silica particle additions to the silica sol using a pressure infiltration technique, and the drying rate and matrix cracking were characterized. The particle size was varied in order to study the role of particle additions in the processing. Ammonium hydroxide (NH4OH) and a particle coating agent, 3‐(trimethoxysilyl)propyl methacrylate (TPM), were added in the mixture of particles and sol to improve particle packing in the preform. Sol‐gel processing with the addition of particles proves to be an effective route to fabricate 3‐D ceramic‐matrix composites with higher green density and less matrix cracking.

Thermal expansion behavior and macrostrain of Al2O3/Al composites with interpenetrating networks

The aim of the study is to investigate the thermal expansion behavior and internal residual strains in metal reinforced ceramic matrix composites (CMCs). A variety of Al2O3/Al CMCs with an interpenetrating network structure were produced using a pressure infiltration technique. The samples contained two variations in the average ligament diameter of the metal phase of 0.15 μm and 1 μm and metal contents ranging from 13 to 40 vol.%. Coefficients of thermal expansion (CTEs) were found to vary significantly with temperature. It is proposed that this indicates an influence of the flow characteristics of the metal. Comparisons are made with well known methods for predicting CTEs of metal/ceramic composites. Overall strain increases with temperature scaled proportionally with metal content. Comparisons were made with uninfiltrated porous ceramic preforms and a pure metal sample. Hysteresis was observed between the heating and cooling of the composite samples at constant rate.

Pressure infiltration technique for synthesis of aluminum–fly ash particulate composite

Beds of nickel coated and uncoated cenosphere fly ash can be successfully infiltrated by molten aluminum under very low pressures. The density of the resultant composite is ≈1.4 and 1.2 g cm −3 respectively, compared to 2.68 g cm −3, the density for aluminum. The threshold pressure was found to be between 20.68 and 27.58 kPa for infiltration of molten pure aluminum into uncoated fly ash, and around 6.7 kPa for Ni-coated fly ash. These data were used to back calculate an effective wetting angle between molten pure aluminum and fly ash using Young’s and Washburn equations. The average value of the wetting angle calculated for uncoated fly ash is 111°. The microstructures and chemical composition of the composites made with coated and uncoated fly ash were studied using optical and scanning microscopy; they show good infiltration except for regions between contacting cenospheres. They also show transport of nickel from the bottom to the top of the sample when nickel coated particles were used.

Effect of Surfactants on Pressure Infiltration of Calcium Chloride Solutions into `Golden Delicious' Apples

The effects of 36 organosilicone and conventional carbon-based surfactants on postharvest infiltration of radiolabeled and unlabeled Ca solutions into `Golden Delicious' apples (Malus domestica Borkh) were examined to devise a more efficient pressure infiltration technique to increase fruit Ca concentration. Radiolabeled Ca infiltration and the proportional increase in fruit Ca estimated by fruit weight gain from Ca solutions of known concentration were significantly enhanced by a range of surfactants having different chemical structures. Tween 60 and 80; Triton X-45, X-100, X-114, X-305, and X-405; and Silwet L-77 and L-7604 enhanced Ca infiltration. The two organosilicone surfactants, Silwet L-77 and Silwet L-7604, known for their greater capacity to lower the surface tension of solutions than conventional carbon-based surfactants, were the most effective at augmenting Ca infiltration. Applications of surfactants to fruit were as or more effective when used as a pretreatment rather than mixing the surfactant with the Ca solutions. The pressure necessary to increase Ca to levels considered sufficient to maintain fruit firmness and resist decay during storage could be lowered in fruit treated with organosilicone surfactants. Sequential postharvest surfactant and Ca treatments may be a practical means of increasing the Ca concentration in apples.