Oxidation of titanium carbide-graphite hetero-modulus ceramics with low carbon content II. Physico-chemical interpretation of the ridge effect

Hetero-modulus ceramics (HMG) present the combination of a ceramic matrix with the inclusions of a dispersed phase with considerably lower Young's modulus, resulting in a material with significantly improved properties. An interpretation of the so-called ridge effect observed during the isobaric-isothermal oxidation of 93 vol% TiC-7 vol% C (graphite) HMC at temperatures of 400-1000 degrees C and oxygen pressures of 0.13-65kPa is given. Established in Part I of this study, the meanings of a ridge temperature and ridge oxygen pressure, which are served as boundaries between prevailing oxidation mechanisms in phenomenological kinetics model, are considered on the basis of X-ray diffraction (XRD) and microscopy analyses. The oxidation mechanisms, essentially different within the studied ranges of temperatures and oxygen pressures are identified according to the developed general model. These results can be used for the preparation of special protective coatings on the surface of refractory carbide-carbon HMC parts applied in severe environments, e.g. chemically active, high-enthalpy gaseous flows. (c) 2008 Elsevier Ltd. All rights reserved.