Oxidation resistance of a gradient self-healing coating for carbon/carbon composites

A gradient self-healing coating consisting of three layers, SiC-B4C/SiC/SiO2, was examined as a multilayer protection for carbon/carbon composites. The inner layer was made of B4C and beta-SiC, the middle layer was a SiC based layer, and the outer layer was SiO2 as an airproof layer. Both inner and middle layers were produced to be diphase structure by a pack cementation technique, and the outer airproof layer was prepared by hydrolyzing tetraethylorthosilicate. SEM and EDS investigations showed that the coating had a compositional gradient between B4C and SiC. The coating showed great self-healing properties from 500 degrees C to 1500 degrees C. The weight loss rate of the coated composites was less than 1.3% after 50 h at 1500 degrees C, and coating represented excellent thermal shock resistance at 1500 degrees C. The oxidation kinetics of coated carbon/carbon composites showed that the Arrhenius curve consisted of three parts with two broken points at about 700 degrees C and 1100 degrees C, and the three parts corresponded to three different self-healing mechanisms in different temperature regions. (C) 2007 Elsevier Ltd. All rights reserved.