Diffusion-Controlled Oxidation of Binary Alloys with Special Reference to Nickel-Iron Alloys

Abstract

<p> This investigation is concerned with the development of a general ternary diffusion analysis for the diffusion-controlled oxidation of binary alloys based on the concept of local equilibrium and phenomenological diffusion theory and its application to appropriate experimental systems. </p> <p> The theoretical analysis is in two parts. In the first part diffusion equations for the alloy and oxide phases are obtained and tested against experiments for Ni-10.9% Co alloy at 1000°C. In the second part phenomena observed in binary alloy oxidation such as supersaturation, internal oxidation and morphological instability are qualitatively discussed and the concept ot the stationary diffusion path on the isotherm is applied to binary alloy oxidation. In general the ternary diffusion analysis satisfactorily accounts for the diffusion-controlled oxidation properties of several binary alloys. </p> <p> An experimental investigation of the oxidation of nickel-iron alloys at 1000°C is described. In the first part of the experimental investigation, thermodynamics of the ternary iron-nickel-oxygen system at 1000°C has been investigated in support of the oxidation studies. The second part is comprised of a detailed kinetic and metallographic study of nickel-iron alloys containing upto 25% iron exposed to oxygen atmospheres at 1000°C and determination of the metal concentration profiles in the oxide and alloy phases. The experimental results for these alloys are in good agreement with the theoretical calculations. </p>