| Abstract: | Effect of 1% Zr on oxidation behaviour of Fe-15 Cr-4 Al alloy under isothermal conditions in air, O2 and O2-10% H2O environments in the temperature range 1000–1150°C was investigated. The effect of zirconium concentration was studied at 1 200°C in air. Oxidation rate increases with increase in zirconium concentration. Parabolic rate of oxidation was observed. Limited study on cyclic oxidation was carried out at 1150°C in air. The cycle consisted of one hour holding at isothermal temperature followed by half an hour air cooling. The oxidised samples were examined by X-Ray diffractometry, SEM, EDAX. Extensive spalling was observed in the base alloy, Fe-15 Cr-4 Al in all environments. Zirconium additions eliminated the spalling of the scale. The EDAX analysis of a spalled region shows the presence of iron and chromium while the unspalled region is aluminium rich. A common structural feature, localised formation of granules/nodules was observed in the scale of zirconium containing alloys in all the environments. The number of granules increased with increase in zirconium concentration and was observed to be a maximum in 1% Zr and also increases with increasing temperature. The observations reveal that 1% Zr alloy shows lower oxidation rate in O2-H2O environment under isothermal conditions. X-Ray diffraction analysis shows the additional presence of Fe2O3 and Cr2O3 in α-Al2O3 scale which have not been detected in the α-Al2O3 scale formed in other environments, air and O2. 0.2% Zr is most effective in increasing oxidation resistance of Fe-15 Cr-4 Al alloy both under isothermal and cyclic oxidation conditions. |
