Oxidation behavior of hot pressed ZrB2-SiC and HfB2-SiC composites

Non-isothermal isothermal and cyclic oxidation behavior of hot pressed ZrB2-20 (vol %) SiC (ZS) and HfB2-20 SiC (HS) composites have been compared Studies involving heating in thermogravimetric analyzer have shown sharp mass increases at 740 and 1180 degrees C for ZS and mass gain till 1100 degrees C followed by loss for HS Isothermal oxidation tests for 1, 24 and 100 h durations at 1200 or 1300 degrees C have shown formation of partially and completely stable oxide scales after similar to 24 h exposure for ZS and HS, respectively X ray diffraction, scanning electron microscopy and energy or wavelength dispersive spectroscopy has confirmed presence of ZrO2 or HfO2 in oxide scales of ZS or HS respectively besides B2O3-SiO2 Degradation appears more severe in isothermally oxidized ZS due to phase transformations in ZrO2, and is worse in HS on cyclic oxidation at 1300 degrees C with air cooling because of higher thermal residual stresses in its oxide scale (C) 2010 Elsevier Ltd All rights reserved