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.
Record created on 2015-07-09, modified on 2016-08-09