Oxidation of Zirconium and Zr + 1% Nb Alloy in Air under Nonstationary Conditions

ISSN： 1068-820X

Source： Materials Science, Vol.36, Iss.5, 2000-09, pp. : 683-688

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Abstract

We present some results of the experimental investigation of the influence of thermal cycling on the kinetics of interaction of zirconium iodide and KTTs-110 (Zr–1% Nb) alloy with air. The tests were carried out both in the stage of heating to 1000°C and in the course of long-term (6 h) holding for the mean temperatures T = 750, 800, 950°C (970°C) and the amplitude of thermal cycles 100°C (±50°C). We measured the specific increment of mass of the metal specimens (per unit area of the surface), the thickness and state of the surface films, and the microhardness of the metal surface. The results obtained in the course of cyclic variation of temperature were compared with similar data accumulated in the process of heating at a constant rate followed by isothermal holding. It is shown that thermal cycling with holding in the α-region intensifies the processes of gas saturation and oxide formation promoting the redistribution of the diffusing substance between the oxide film and the diffusion zone in favor of the latter. The process of thermal cycling in the -region results in the catastrophic oxidation of both zirconium iodide and the KTTs alloy and, in the case of rapid heating, decreases the rate of interaction due to the stabilization of the high-temperature phase with enhanced protective properties. It is possible to conclude that the procedure of thermal cycling may intensify the processes accompanying the thermochemical treatment of products made of zirconium alloys.