In the present paper the effect of gas flow rate on the high temperature oxidation behaviour of the three Ni-base alloys 230, X and 625 in wet air will be presented. For the studies two different gas velocities were used, i.e. near static conditions (5·10-3 m/s) and a gas flow rate of 0.7 m/s. The oxidation kinetics was studied by gravimetry during cyclic testing at 900 and 1000°C. The oxide scales and the subsurface depletion zones formed during oxidation were studied by light optical microscopy and scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX). It was found that Cr loss due to formation of volatile species may be substantially enhanced by high gas flow thus dramatically influencing the oxidation limited life time of the oxidising component. Additionally it was found that geometrical factors of the test specimen substantially affected the extent of volatile species formation; especially the specimen leading edge exhibited more extensive formation of volatile Cr species than other specimen areas.
Using the measured oxidation kinetics the subscale depletion processes and microstructural changes were modelled using a Calphad based approach aiming at a prediction of oxidation limited life as function of flow rate and component geometry.