Thermal oxidation kinetics and oxide scale adhesion of Fe-15Cr alloys as a function of their silicon content

Three types of Fe-15Cr alloys, containing 0,0.5 and 1 wt.% Si, were studied between 850 and 950 degrees C in terms of oxidation kinetics, oxide spallation and oxide adhesion energy. The oxidation kinetics in Ar-15% O-2 were found to be parabolic, exhibiting non-monotonic evolution of the parabolic rate constant with increasing Si content, with a minimum value for 0.5% Si. Chromia scale spallation on cooling was quantified as a function of oxide thickness, showing again non-monotonic behaviour, with no spallation for the Si-free alloy, up to a scale thickness of 2.7 mu m, and maximum spallation for the 0.5% Si alloy. Room temperature tensile testing in a scanning electron microscope chamber was used to quantify oxide adhesion. Interfacial fracture energy values derived from these experiments were shown to be in the range 20-80 J m(-2), with the respective values in good agreement with the observation of spallation during cooling. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.