The Internal Oxidation of Ternary Alloys. IV: The Internal Oxidation of the Most-Reactive Component Beneath External Scales of the Component Having Intermediate Reactivity

The kinetics of internal oxidation of the most-reactive component C of ternary A–B–C alloys in the presence of external scales of the oxide of the component of intermediate reactivity B, BOν, are examined using convenient approximations. The precipitation of the most-stable oxide leaves behind a matrix composed of a mixture of the two most-noble components, A and B, whose composition changes with depth due to the consumption of B to form the external scale. For the calculation of the parabolic rate constant use is made of approximate expressions for the concentration of oxygen dissolved in the binary A–B metal matrix within the zone of internal oxidation and for the diffusion coefficient of oxygen as functions of the alloy composition. Numerical calculations of the parabolic rate constant of internal oxidation are carried out for different combinations of values of the various parameters involved. The results obtained for the ternary alloys are compared with the corresponding data calculated for the binary A–C and B–C alloys under the same conditions.