Polyfunctional Interface Coatings for High Temperature Resistant Ceramic Composite of SiC/SiC Type

摘要

Preliminary results are presented of fabricating protective MoSi_2 coating and so called "Theological" SiC coating on both SiC/C and SiC-coreless fibres. The study is carried out in order to solve one of the major problems in creating a high oxidation resistant ceramic matrix composites (CMC) of SiC/SiC type for a long work at 1800 - 2100 K. Chemical vapour deposition (CVD), reactive vapour deposition (RVD) and preceramic polymer deposition (PPD) were explored. The fibres of Nicalon and SiC/C types were coated. CVD protective coatings deposited under mild regime (< 1100 K ) in the system of Mo(CO)_6 and SiH_4 had a multiphase composition: MoSi_2, Mo_5Si_3, Si and Mo were identified by XRD. A consecutive deposition of Mo- and Si-layers followed by a heat treatment demonstrated the impossibility of coating the Nicalon first with Mo-layer. Molybdenum disappeared quickly at heat treatment working temperatures due to interaction with initial oxygen of coreless SiC-fibres. The experiments with Hi-Nicalon (not more than 0.8 mass. % of O_2) are under study now. The best results were got by RVD with SiC/C-fibres, when a layer of Mo was silicided with SiCLt. At the same time a new complication was revealed: the formation of pores in the layer induced by interdiffusion. The results demonstrate two interconnected problems: the protection of fibres from environment and the perfection of their internal composition and structure. The Theological SiC-coating on the Nicalon fibre was successfully prepared by polymer pyrolysis deposition (PPD).