Cyclic Oxidation Behaviour of a Ni-Based Alloy at 900°C

The cyclic oxidation behaviour of Ni 5.5Al 2.6Ti 4.8Co 3.9Mo 5.0W 11.0Cr superalloy at 900 °C in air has been investigated by means of measuring the kinetics curves of the oxidation and analysis method of XRD and SEM/EDAX. The results show that the mass gain rapidly increases in the initial stage, and the weight loss and mass gain occurs alternately during the cyclic oxidation. An obvious oxidation and internal oxidation occurs during cyclic oxidation. Ti in the alloy oxidized, diffusing through the Al2O3 and Cr2O3 scales to form faceted TiO2 particle on the surface of the alloy. Al2O3 formed discontinuousness inner oxides in the alloy.

Effects of Water Vapour on the Oxidation of Chromia Formers

Water vapour interacts with growing chromia scales in several different ways. Formation and volatilisation of Cr2O2(OH)2 is shown to account quantitatively for chromium loss from thin alloy foils reacted with air-steam mixtures over periods of 103 h. In the shorter term, water vapour is shown to refine the grain structure of Cr2O3 scales grown on Ni-25Cr. Scaling kinetics are at the same time accelerated by an additional, larger contribution to diffusion by a grain boundary species, either OH- or H2O. A slight increase in scaling rate observed at low water vapour partial pressures in H2/H2O gases is thought to be due to hydrogen doping.