R, Naslain nD. DRY FIBER PREF INTERPHASE INFILTRATION short Pyc BN (PyCSiC)n MATRIX INFILTRATION MTS·H vp=10.15% SEAL COATING INFILTRATION MTSH2 SiC or multilayer coating near net shape CMCs Figure 4. Fabrication of near net shape non-oxide composites(C/C: C/SiC; SiC/SiC and related materials) by CvI (schematic flow chart) oxides or oxides)[35, 631. It has been transferred to the plant level for the production of C/C, C/SiC and SiC/SiC composites 3.2.2. Rapid CVI process. The densification rate can be significantly improved when mass transfer in the preform occurs by fast convection (instead of slow diffusion) and the temperature is raised. This is usually achieved by applying a temperature gradient(TG-CVI) or/and a pressure gradient(F-CVD)to the preform Unfortunately, these improved CVI-techniques are less flexible than I-CVI[64-701 3.2.3. Pressure-pulsed CVI (P-CV1). In P-CVL. reactants and products are respectively injected in the reactor and removed by pumping, in a periodic manner When the duration of each pulse is short enough, i.e. of the order of a second. the deposit can be built almost atomic layer by atomic layer [71-73]. Further, if the nature of the precursor is periodically changed, multilayered ceramics where the elementary layer thickness can be of the order of a few nm, can be deposited in a porous preform. (PyC-SiC) or(BN-SiC)m interphases, as well as self- healing matrices have been produced by P-CVI in SiC (or C)fiber composites to increase the lifetime in oxidizing atmospheres(Figs Ic. 2. 5)133, 34, 74 .Hence, the P-CVD/CVI is a powerful tool to engineer multilayered ceramics at different scales(ranging from the nm- to the um-scales). As an example. it has been shown that P-CVD/CVI can be used to fabricate(PyC-SiC) multilayered ceramics mimicking the layered structure of nacre in seashells [751