The effect of niobium on the oxidation behaviour of titanium in N2/20% O2 atmospheres

A systematic study on the isothermal oxidation of Ti-based materials, i.e. pure Ti, Ti–4at.%Nb, and niobium implanted Ti, was conducted in order to obtain more insight into the role of small amounts of niobium on the oxidation of niobium-containing intermetallic alloys. Examinations were performed by thermogravimetry and by studying the surface morphology, structure and composition of the oxidation products. Hardness measurements were made to quantify the amount of dissolved oxygen in the metallic matrix. Oxidation experiments performed in dry and humidified nitrogen/oxygen atmospheres at 800°C showed that the presence of niobium not only significantly reduced the growth of titania, but also significantly reduced the influence of water on the oxidation behaviour of Ti. This beneficial effect was explained by the formation of a continuous nitride layer, already during the initial stage of the oxidation, at the scale/substrate interface, induced by the presence of small amounts of niobium.