The thermal gradient - pulse flow CVI process : A new chemical vapor infiltration technique for the densification of preforms
Résumé
Three-dimensional carbon fibre preforms were infiltrated with pyrocarbon or silicon carbide using a new process which combines a thermal gradient variation with a pressure pulsed chemical vapor infiltration. In this work, the principle of this TP-CVI process is presented. Thermal evaluations are carried out as guidelines to set up a model. Experimental infiltrations were performed, to validate the model. A comparison with experiments performed by P-CVI (i.e. without thermal gradient) shows that the TP-CVI process yields a better in-depth densification of the preform and a better deposit homogeneity. The thickness gradient depends chiefly on the thermal quenching ΔT. Process and equipment improvements led to samples more densified in the core than near the surface, that is, to samples still densifiable after considerable densification. This new technique also allows the use of preforms with higher fibre volume fractions. Three-dimensional carbon fibre preforms were infiltrated with pyrocarbon or silicon carbide using a new process which combines a thermal gradient variation with a pressure pulsed chemical vapor infiltration. In this work, the principle of this TP-CVI process is presented. Thermal evaluations are carried out as guidelines to set up a model. Experimental infiltrations were performed, to validate the model. A comparison with experiments performed by P-CVI (i.e. without thermal gradient) shows that the TP-CVI process yields a better in-depth densification of the preform and a better deposit homogeneity. The thickness gradient depends chiefly on the thermal quenching ΔT. Process and equipment improvements led to samples more densified in the core than near the surface, that is, to samples still densifiable after considerable densification. This new technique also allows the use of preforms with higher fibre volume fractions.