High-temperature OM investigation of the early stage of (TiC+TiB)/Ti oxidation

The initial oxidation behavior of titanium matrix composites (TMCs) was studied in a temperature range 550 to 650◦C in a flow of purified oxygen at atmospheric pressure using thermogravimetry. The oxidation kinetics very initially follows approximately a linear rate law and then a parabolic rate law. The oxidation rate decreases gradually as the oxidation proceeds. The initial in situ oxidation was investigated by high-temperature optical microscopy in air. The oxide layer was examined by X-ray diffraction and scanning electron microscopy combined with an energy dispersive X-ray spectroscopy unit. It was found that the reaction products are predominantly rutile. The reinforcements of TiB and TiC can result in a decrease in the overall oxidation rate at 550, 600, and 650◦C. This is attributed to the interface cohesion and the clean interfacial microstructure between reinforcements and the titanium matrix alloy, which is strong enough such that the reinforcements can act as barriers to solid-state diffusion. C 2005 Springer Science + Business Media, Inc