Capillarity in pressure infiltration: influence of percolation and wetting angle

Composite materials are often produced by pressure-infiltration of a liquid matrix into a preform of packed solid fibers or particles. Capillary forces that intervene in this process are quantified by measuring saturation curves, which are plots of the fraction pore space filled with the matrix versus the pressure difference between the matrix and the atmosphere initially present in the porous preform to be infiltrated. We have constructed an apparatus capable of measuring saturation curves at high temperature (≈1000°C) and high pressures (≈100 atmospheres), which is suitable for the study of metal matrix composite pressure infiltration. Using this apparatus, we study the metal flow path during infiltration, exploring both early and later stages of the process. We measure the effect of capillary parameters derived from sessile drop experiments and known to govern the wetting of ceramics by molten metals, placing focus on copper and its alloys infiltrating preforms of alumina or carbon. We show that initial phases of the process display universal scaling and fractal geometric features that are characteristic signatures of percolation-dominated wetting; later stages of the process obey the Brooks and Corey correlation. We explore the influence of the contact angle and work of immersion by measuring pressure/saturation curves for the infiltration of packed alumina particle preforms by liquid Cu-Al, Cu-Sn and Sn-Al alloys and seek explanations for the observed dependence by means of a network model constructed to combine simplicity with a realistic description of governing microscopic capillary phenomena.

Influence of temperature and wetting angle on capillarity in pressure infiltration

William Craig Carter, Alain Léger, Andreas Mortensen, Gionata Schneider, Ludger Weber

Capillary forces in the pressure infiltration process can be quantified by measuring saturation curves; these are plots of the fraction pore space filled with the liquid infiltrant versus the pressure difference between the liquid and the atmosphere initially present in the porous preform to be infiltrated. We present data measured using an apparatus capable of measuring saturation curves at high temperature (≈1200°C) and high pressures (≈150 atmospheres), these being conditions suitable for the study of metal matrix composite pressure infiltration. Preforms of alumina or carbon are infiltrated with copper-based melts, varying the infiltration temperature and the alloy composition, to explore (i) the influence of the contact angle and work of immersion (reported in the literature from sessile drop experiments) on the saturation curve and consequently the ease of infiltration processing for the various systems explored and (ii) sources of irreversibility in the process that arise from geometrical and kinetic features of the infiltration process.

2015

Capillarity in pressure infiltration: improvements in characterization of high-temperature systems

Claudio Bacciarini, Raphaël Charvet, Willy Dufour, Alain Léger, Andreas Mortensen, Noelia Rojo Calderon, Ludger Weber

In the pressure infiltration of metal matrix composites, molten metal is injected under external pressure into a porous preform of the reinforcing material. Equilibrium capillary parameters characterizing wetting for this process are summarized in plots of metal saturation versus applied pressure, also known as drainage curves. Such curves can be measured in our laboratory during a single experiment with an infiltration apparatus designed to track the rate of metal penetration into porous preforms under conditions characteristic of metal matrix composite processing (temperatures in excess of 1000 A degrees C and pressures in the order of 10 MPa). For such measurements to be valid, infiltration of the preform with molten metal must be mechanically quasi-static, i.e., the metal must flow at a rate sufficiently low for the metal pressure to be essentially uniform across the preform at all times. We examine this requirement quantitatively, using a finite-difference model that simulates the unsaturated unidirectional ingress of molten metal into a ceramic particle preform of finite width. We furthermore present improvements in the experimental apparatus developed in our laboratory to measure the entire drainage curve in a single experiment. We compare numerical results with new experimental data for the copper/alumina system to show (i) that pressurization rates sufficiently low for quasi-static infiltration can be produced with this apparatus, and (ii) that taking the relative permeability equal to the saturation yields better agreement with experiment than does the expression originally proposed by Brooks and Corey.

Springer Verlag2012

Percolation and Universal Scaling in Composite Infiltration Processing

Alain Léger, Andreas Mortensen, Ludger Weber

Composite materials are often made by infiltration, that is, by injecting a liquid matrix between packed solid fibers or particles. We give here direct proof that molten copper, slowly infiltrated into a broad spectrum of preforms, displays in initial phases of the process universal scaling and fractal geometric features that are characteristic signatures of percolation-dominated flow. Implications are that the microstructure of infiltrated composite materials can develop over length scales that far exceed the average preform pore size, and that network models are pertinent in the simulation of composite infiltration processing. © 2014 The Author(s). Published by Taylor & Francis.

2014