The effect of niobium on the oxidation behavior of titanium in Ar/20% O-2 atmospheres

The effect of niobium was studied on the isothermal oxidation of pure titan ium under well-controlled environmental conditions. This material was chose n as a model system to obtain more information of the exact role of niobium on the oxidation of niobium-containing intermetallics. Several studies hav e already been undertaken to investigate and reveal the mechanism behind th e beneficial effect of niobium on the oxidation behavior of gamma-TiAl-base alloys. However, due to the complexity of these systems, including often m ore than one reactive gas compound and alloys with more than one constituen t, it is difficult or sometimes impossible to draw conclusions. In order to avoid synergistic effects (effects between different gas compounds in the gas atmospheres and material constituents), a systematic study on the isoth ermal oxidation of Ti-base materials, i.e., pure Ti, Ti-4(at.%)Nb, and niob ium-implanted Ti, was performed. Oxidation experiments performed in dry and humidified argon/oxygen atmospheres at 800 degrees C showed that the prese nce of niobium not only significantly reduced the growth of titania, but al so significantly reduced the water effect, as found during oxidation of pur e Ti under humidified conditions. On the other hand, because of the presenc e of niobium, the amount of oxygen dissolved in the underlying metallic mat rix and the maximum penetration depth of oxygen in the underlying substrate was higher. In addition, the process of cracking, inducing the formation o f a lamellar structure of the oxide scale, was slightly affected by the pre sence niobium.