Capillary forces are of primary importance in materials processing and this is particularly true in metal-matrix composite (MMC) production by liquid metal infiltration. In this process, molten metal fills a porous preform of the reinforcement phase, after which it is solidified within the preform pores, resulting in a composite material. In liquid metal infiltration, spontaneous infiltration is rarely observed: external force must generally be applied to drive the molten metal into the preform. As result, most infiltrated metal matrix composites are produced by pressure infiltration.
Capillarity is thus crucial in this process; however, as infiltration is a dynamic process, equilibrium wetting data in the literature (mostly from sessile drop experiments) are of questionable relevance. With an infiltration apparatus designed to measure dynamically the rate of metal penetration (such as Cu) during infiltration of porous preforms (made typically of Al2O3) at high temperature (up to 1300°C) and high pressure (up to 10 MPa), capillary parameters characterizing wetting under conditions more directly related to infiltration can be measured. Data take the form of drainage curves (plots of volume fraction of metal in the preform as a function of applied pressure as measured after equilibration), that can be measured in a single infiltration experiment. The system comprises a graphite plunger floating atop the liquid metal. When infiltration starts, the plunger moves with the metal, such that by measuring its displacement, the saturation can be directly deduced as a function of time and pressure. Measuring motion of the floater is accomplished via a new optical system, featuring two (pressure and vacuum resistant) custom-made windows, one for a light source and the other for capture by a digital camera of a series of white stripes lining the rod that connects the rotative and vibrative systems to the graphite plunger. A dedicated LabView software was developed to compute the metal level position by image analysis. The resolution of the system is in the order of several micrometres while the precision (after calibration) is around 40-50 µm for a 6 mm displacement of the graphite plunger. This apparatus allow us to work in a broad range of experimental conditions, including pressurization rates spanning the range from 10-1 to 10-4 MPa/s while maintaining high temperatures stable within a few degrees (±5ºC at 1300ºC).
The presentation will detail these new developments to the technique, showing how these improve on both the range of conditions that can be explored and the precision in data collected. Conditions for quasistatic infiltration will also be detailed based on experiment and numerical analysis and new data will be presented on the infiltration of alumina preforms with alloys of copper selected among those for which sessile drop data exist.