Formation and Mechanism of Carbon-Containing Oxide Scales by Oxidation of Carbides (ZrC, HfC, TiC)

摘要

The isothermal oxidation of carbide single crystals (ZrC, HfC, TiC) with the 200 or 220 face was carried out at 700 to 1500 and at oxygen pressures of 0.08 to 80 kPa. The oxidation, which was determined from the weight changes, was described by linear kinetics. The preferred {200} or {220} orientation of ZrO_2, HfO_2, and Ti_3O_5 was detected by XRD. The duplex oxide scale was found to consist of an almost compact, pore-free scale (zone 1) and a porous, cracked scale (zone 2). Zone 1 contained 20 - 25 at. % elemental carbon and zone 6 to 11 at.% carbon. Zone 1 grew parabolically and zone 2 thickened linearly. The interface between zone 1 and the carbide was observed by SEM and HRTEM to reveal the microstructure and morphology of zone 1. The formation mechanism of carbon-containing scales (zones 1 and 2) was derived from kinetic considerations and interfacial observations.