Recent advances in modeling of chemical vapor infiltration

Modeling of the chemical vapor infiltration (CVI) process has progressed significantly over the past decade. One model developed at Georgia Tech has been used successfully for both isobaric-isothermal and forced flow-thermal gradient processes for fabrication of SiC matrix-Nicalon fiber composites, and to a more limited extent for TiB2 and carbon matrix composites with carbon fiber reinforcement. Extension to other matrix materials is limited by the general lack of suitable kinetics parameters. However, recent work in experimental and model determination of preform transport properties will allow wider exploration of different reinforcement fiber architectures. Model simulations suggest that two relatively undeveloped variations of the CVI process may offer advantages. The forced flow-isothermal process using alternating flow directions yields rapid densification with relatively simple equipment requirements. Secondly, a hybrid of forced flow and isobaric processing with a thermal gradient yields rapid densification and a high density, gas-tight material.