Infiltration of fibrous preforms by a pure metal: Part I. Theory

General expressions are derived to describe fluid flow and heat transfer during infiltration of fibrous preforms by a pure metal. Analytical solutions to the problem are given for the case of unidirectional infiltration into a uniform preform of aligned fibers under constant applied pressure. Calculations are carried out for infiltration kinetics (including total infiltrated length) and temperature distribution, using as an example alumina fiber/aluminum composites. Limiting cases leads to very simple expressions. Initial fiber temperatures both above and below the metal melting point are considered. In the case of fibers at a temperature significantly below the metal melting point, it is concluded that the factor most strongly influencing infiltration is the solidification of metal in the interfiber region. In the calculations, it is assumed that this solidification is in the form of a uniform solid metal sheath around the fibers. Metal superheat, when present, serves to progressively remelt the solidified sheath from the upstream end of the preform. Fiber volume fraction and initial temperature are predicted to have a major effect on infiltration kinetics, while metal superheat exerts a relatively minor influence. When no external heat extraction is present and a constant pressure is applied to the metal, flow through the preform continues indefinitely. For the case of external heat extraction, flow ceases when sufficient solidification occurs to block flow. L.J. MASUR, formerly a Graduate Student with the Department of Materials Science and Engineering, Massachusetts Institute of Technology