希薄Ni-Ti合金の内部酸化と酸化物粒子

抄録

The kinetics of internal oxidation of a Ni-0.26%Ti alloy has been investigated in the temperature range from 1273 to 1573 K, and the morphologies and structures of the oxide particles formed have been studied by electron microscopy of extraction replicas.
The kinetics of internal oxidation was well described by Wagner’s equation, that is, the penetration rate of the internal oxidation front is determined by the diffusion of the dissolved oxygen. The oxide particle size increased with distance from the specimen surface, but small particles were observed near the oxidation front. The shape of oxide particles was various: needle-like, plate-like and massive. Four kinds of oxides were recognized: NiTiO₃, TiO₂ (rutile), TiO₂ (brookite) and TiO (NaCl type). NiTiO₃ was mostly observed near the specimen surface. Rutile was generally observed throughout the internal oxidation zone and brookite only in a few cases. TiO was recognized among the small particles present near the oxidation front. Twins with {101} twinning plane and planar defects were often seen in some rutile particles. Especially, a rutile particle, which was near the oxidation front, showed a defects structure of many twins and planar defects similar to those seen in a slightly reduced rutile, TiO_2−δ.