J. Narciso

Pressure infiltration of packed ceramic particulates by liquid metals

The work carried out on pressure infiltration of packed ceramic particulate by liquid metals, mainly aluminum and its alloys, is reviewed. The theoretical background and the main features of the technique and of the experimental procedures are first considered. The experimental results obtained by several authors approximately follow Darcy and capillary laws. The distinguishable roles of the key variables of the infiltration process are illustrated by means of selected experimental results. These variables can be classified according to their origin: (a) ceramic particulate (size and shape, surface condition); (b) liquid metal (surface tension, etc.); (c) liquid/solid interface (contact angle, reactivity, etc.); and (d) experimental variables (pressure, temperature, etc.). In particular, the importance of the particulate shape and size distribution, the surface tension of the liquid metal, the contact angle, and the oxide layer, in the case of aluminum, is highlighted. Results for binary aluminum alloys and alloys of technological interest (AlMgSi and AlCu alloys) are also discussed. Comparison of results for other metals with those for aluminum throws light on several aspects of the infiltration process. Of particular interest is silver, a metal having a behavior with respect to oxygen opposite to that of aluminum.

Thermal expansion behaviour of aluminium/SiC composites with bimodal particle distributions

The thermal response and the coefficient of thermal expansion (CTE) of aluminium matrix composites having high volume fractions of SiC particulate have been investigated. The composites were produced by infiltrating liquid aluminium into preforms made either from a single particle size, or by mixing and packing SiC particulate of two largely different average diameters (170 and 16 μm, respectively). The experimental results for composites with a single particle size indicate that the hysteresis in the thermal strain response curves is proportional to the square root of the particle surface area per unit volume of metal matrix, in agreement with current theories. Instead, no simple relationship is found between the hysteresis and any of the system parameters for composites with bimodal particle distributions. On the other hand, the overall CTE is shown to be mainly determined by the composite compactness or total particle volume fraction; neither the particle average size nor the particle size distribution seem to affect the overall CTE. This result is in full agreement with published numerical results obtained from finite element analyses of the effective CTE of aluminum matrix composites. Our results also indicate that the CTE varies with particle volume fraction at a pace higher than predicted by theory.

Pressure infiltration of liquid aluminium into packed SiC particulate with a bimodal size distribution

Abstract High volume fraction composites were produced by infiltrating liquid aluminium into preforms made by mixing and packing SiC particles with average diameters of 170 and 16 μm. The maximum particle volume fraction (0.74) was attained for a mixture having 67% of coarse particles. The variation of the preform compactness with the percentage of coarse particles can be reasonably well understood in terms of a simple model. The experimental results indicate that the threshold pressure is mainly determined by the local compactness of fine particles, a result which is shown to be compatible with the model used to calculate the particle volume fraction. The permeability of the compacts was also evaluated by means of pressureless infiltration with an organic liquid (polyethylene glycol) and the results were compared with those obtained with aluminium. The two data sets qualitatively agree for low percentages of coarse particles. However, while the permeability obtained with the organic liquid shows a minimum for preforms having the maximum compactness (roughly half the value obtained for fine particles), in the case of aluminium, the permeability for that preform (and others having a compactness around the maximum) was significantly higher. This was ascribed to the pushing of particles during pressurised infiltration of aluminium, triggered by particle segregation.

Factors affecting pressure infiltration of packed SiC particulates by liquid aluminum

Pressure infiltration is being currently used to evaluate the wettability of ceramic particles and fibers by liquid metals. The objective of this work is to investigate the effect of type and surface condition of the particulates and infiltration atmosphere on pressure infiltration of packed SiC particulates by pure liquid aluminum. Fourteen SiC particulates from five different suppliers, of green (high purity) and black (low purity) types, were used. Two of the particulates were subjected to either low- or high-temperature heat treatments in order to either burn organic residues or promote oxidation. Infiltrations were carried out in air, argon, argon/hydrogen, and nitrogen/hydrogen atmospheres. The results indicate that the threshold pressure does not depend appreciably on the type of particulate. A heat treatment at 600 ‡C improves the infiltration performance of particulates having a large amount of organic residues, whereas oxidation at 1000 ‡C decreases the threshold pressure. The results also illustrate the effects of the infiltration atmosphere; in particular, it is shown that inert or reducing atmospheres improve wettability.

A differential scanning calorimetry study of solid state reactions in AA6061SiC, AA6061Al2O3 and A357SiC composites fabricated by means of compocasting

Abstract Phase formation and dissolution in AA6061SiC, AA6061Al2O3 and A357SiC composites have been investigated by means of differential scanning calorimetry (DSC). The composites were fabricated by means of molten metal mixing, extruded and heat treated. The DSC studies were carried out on material in the as-quenched and naturally and artificially aged conditions. In the AA6061 materials the effects of the reinforcement are similar to those observed by other authors. Some remarkable features of the results for the composites are: a smaller amount of Guinier-Preston (GP) zones, a faster precipitation kinetics of the intermediate phases (β″ and β′), and the absence of the peak related to the formation of the β phase. These results are all a consequence of the largely different thermalexpansion coefficients of the ceramic particulates and the host alloy. In contrast, the differences between A357 monolithic and composite materials are much less noticeable. This should be a consequence of the large amount of free Si in A357 which being in the form of particles, makes the monolithic material behave much like a composite.

Evaluation of the wettability of Al-Pb and Al-Sn alloys with SiC and Al2O3 particulates by means of pressure infiltration

The wettability of SiC and Al2O3 particulates by Al-Pb and Al-Sn alloys has been evaluated by means of pressure infiltration. All infiltrations were carried out in air. The resulting threshold pressures decrease logarithmically with the content of the alloying element, similarly to the experimental data for the surface tension of these alloys reported in the literature. In the case of SiC, the threshold pressure decreases with the alloy content at a higher rate than the surface tension. In contrast, although the results for the alumina particulates are less clear, the tendency seems to be the opposite. These results are interpreted in terms of differences in wettability of silicon carbide and alumina particulates by oxidized aluminium-tin and aluminium-lead alloys.

Surface growth for molten silicon infiltration into carbon millimeter-sized channels: Lattice–Boltzmann simulations, experiments and models

The process of liquid silicon infiltration is investigated for channels with radii from

Pressure infiltration of packed Al2O3 particulates by pure silver

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Pressure infiltration in a reactive system : Packed SiC particulates infiltrated by pure silver with dissolved oxygen

to

The Intrinsic Permeability of Packed SiC Particles with Monomodal and Bimodal Size Distributions

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