Thesis (Ph.D.) - Cairo University - Faculty of Engineering - Department of Metallurgical Engineering

Oxidation properties of inhomogeneous pure Ni and its inhomogeneous binary alloys with Cr containing up to 12 wt% Cr in hot air at 1273K are determined through this research. Seven pellets of inhomogeneous pure Ni and binary Ni-Cr alloys with chromium content which ranges from 0.25 to 12 wt%Cr are prepared using conventional powder metallurgy technique. The oxidation kinetics of inhomogeneous pellets of Ni and Ni-Cr alloys, and of inhomogeneous cast-Ni for a total oxidation time of 100 h has been investigated by gravimetric method. The growth rate of the oxide layers has not been found parabolic but starts with high rate and then it gradually decreases till reaching a constant growth rate (linear growth rate). Porous and duplex oxide layers are formed, which are not adherent with the metal substrate due to the cavities formed at the metal/oxide interface. In order to investigate the oxidation behavior in depth, X-ray diffractometry, optical microscopy, scanning electron microscopy and X-ray energy dispersive analysis are conducted. The main result of this research is that the linear growth rate of homogeneous nickel is estimated to be lower than that of inhomogeneous one by about one order of magnitude

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