X-CVI (WITH X = I or P), A UNIQUE PROCESS FOR THE ENGINEERING AND INFILTRATION OF THE INTERPHASE IN SiC-MATRIX COMPOSITES: AN OVERVIEW

摘要

The interphase is a key constituent in ceramic matrix composites (CMCs). Its main role is to transfer the load from the matrix to the fibers, and to protect the fibers against the notch effect resulting from the propagation of cracks. It is admitted that the most appropriate interphase materials are pyrocarbon, PyC, and hexagonal boron nitride, BN, due to their layered crystal structures (with weak interlayer bonding) and chemical compatibility with the fibers. Chemical vapor infiltration (CVI) is the most appropriate (not to say unique) process to deposit the interphase in the open porosity of fiber preforms. It yields, at moderate temperature (i.e. without damaging the fiber), interphase layers of relatively uniform thickness, composition and microtexture, even in complex nD-fiber preforms, when deposited from appropriate gaseous precursors. The case of PyC, BN and PyC(B) interphases deposited respectively from hydrocarbons, BF_3-NH_3 or BCl_3-NH_3-H_2 and BCl_3-C_3H_8-H_2 precursors, according to the isothermal-isobaric (I-CVI) mode, will be first discussed. CVI, when performed under pressure pulsing mode (P-CVI), can be used to deposit multilayered interphases and hence to engineer interphases at the nano-meter scale and to create new multilayered artificial materials, providing a powerful way to optimize the interphase (and the composite) properties. Examples of (X-Y)_n interphases, where X is a mechanical fuse (such as PyC or BN) and Y a ceramic layer (such as SiC, TiC or B_4C), with improved properties, will be presented and discussed, in a second step.