Effect of Cr content on isothermal oxidation behaviour of nano – Y2O3 dispersed ferritic alloys prepared by mechanical alloying and hot isostatic pressing

Abstract

The isothermal oxidation behaviour of 1.0 wt % nano-Y2O3 dispersed 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B),, 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C), and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) alloys (all in wt %) prepared by solid state mechanical alloying route and subsequent consolidation of the milled powder by hot isostatic pressing (HIP) at 1000 °C using 1.2 GPa uniaxial pressure for 1 h have been studied in dry air in the temperature range 700 – 900 ºC for 50 hrs. Evolution of microstructure and phase aggregate of oxide scale during isothermal oxidation were studied using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis. Gross weight-gain kinetics was parabolic in nature with respect to time, with an activation energy range 155-235 kJ/mol. The alloy D which contained 25.5 wt% Cr shows higher oxidation resistance than that of alloy A, alloy Band alloy C that contained in the range of 13.5 to 21.5 wt% Cr. Oxidation rates are shown to be consistent with diffusion control in iron chromium spinel oxide layer. The scale growth was observed with respect to higher temperature. Oxidation mostly occurred by counter-ionic transport of oxygen from ambience to the core and cations (Cr+3 / Fe+3) from the core to the surface predominately through grain boundaries at low temperature (~700 C) and through grain bodies at high temperature (~800-900 C).