Oxidation of TD nickel at 1050 and 1200�C as compared to three grades of nickel of different purity

Abstract

The oxidation of three nickels of different purity, Ni-200 (≈ 4000 ppm impurity), Ni-270 (≈200 ppm), and JM-Ni (≈30 ppm) was compared to that of TD-Ni (≈400 ppm with 24,000 ppm ThO2). The samples were isothermally oxidized in slowly flowing air at 1050 and 1200°C. All nickels were oxidized with major surfaces either polished, ground, annealed at 1120°C and polished, or annealed at 1240°C and polished. Weight change, metal thickness loss, scale thickness, microstructure, and scale texture were examined. In weight change, metal loss, and scale thickness, the TD-Ni was nearly the same as the higher purity grades, JM-Ni and Ni-270, while Ni-200 oxidized approximately twice as much as the others. Grinding and annealing had only second order effects on these aspects of oxidation behavior. On the other hand, in scale microstructure and texture TD-Ni was similar to the lower purity Ni-200 while Ni-270 was similar to JM-Ni. Grinding did not affect the textures of JM-Ni or Ni-270, which Were (001), but changed the textures of Ni-200 and TD-Ni from (Oil) to (031). Annealing did not affect the microstructure of the oxide layers. A two-layer scale was observed only on the TD-Ni and Ni-200. The presence of ThO2 in TD-Ni appears to act as an impurity in oxide scale orientation but does not substantially alter the extent of oxidation.