MODELING AND THE ADAPTIVE SOLUTION OF REACTIVE VAPOR INFILTRATION PROBLEMS

We develop a mathematical model of a reactive vapor infiltration (RVI) process for manufacturing the matrices of fiber-reinforced ceramic co mposites. The model considers the diffusion of silicon at elevated tem perature into a compressed powder pellet of either molybdenum or a mix ture of molybdenum and molybdenum disilicide and its reaction to form the desired molybdenum disilicide matrix. Volume expansion and materia l distortion that may accompany the siliciding reactions are modeled b y considering the materials capable of viscous deformation, for simpli city, and coupling this mechanical model with the reaction-diffusion s ystem. The partial differential system comprising the model is solved by adaptive finite-element software having capabilities for automatic quadtree-structured mesh generation, mesh refinement/coarsening, metho d order variation, and mesh motion. Temporal integration is controlled within a method-of-lines framework by backward difference software. M eshes can be moved to track material distortion or to reduce discretiz ation errors. Computational solutions of one- and two-dimensional prob lems indicate that the adaptive software is a robust and effective too l for addressing composite-processing problems.