100∼68 wt%Ni-Cu合金の高温酸化

Abstract

Studies have been made of the oxidation behavior of nickel-copper alloys containing 100∼68 wt% nickel. Tests were conducted at temperatures in the range of 725∼930°C, under 160 mmHg of oxygen, using a thermal microbalance, X-ray diffraction and metallographic techniques. The results were as follows: (1) Rate studies showed that the rate for 100∼85%Ni alloys could be interpreted in terms of the parabolic rate law. In the 68%-Ni alloy, the parabolic rate law served to interpret the rate data during the initial stages, but after 150∼200 min oxidation, deviations from the parabolic rate law were taken place. (2) X-ray diffraction studies showed that the oxide films on the 100∼85%-Ni alloys consist of almost pure NiO, regardless of the change in oxidation time and temperature. In the case of 68%-Ni alloy, NiO was the main oxide in the film, but Cu2O increased with the rise of temperature and the increase of oxidation time. The deviations from parabolic rate law in the 68%-Ni alloy occurred as a result of such a change in the oxide-film structure. (3) The relation between the oxidation rate and the oxygen pressure in the 68%-Ni alloy was investigated. (4) The theoretical analysis of selective oxidation of alloys proposed by C.Wagner was discussed.