Study of oxidation processes in the alloys of the system Ni-Ta. I. oxidation of the intermetallic compound Ni{sub}3Ta

摘要

Oxidation kinetics of the intermetallic compound Ni{sub}3Ta was studied by thermogravimetry method in air at temperatures 600-1000 ℃. Isotermal kinetic curves are approximated by parabolic equation. Value of rate constant describing theparabolic oxidation was revealed to be characterized by the periodical increase at temperatures≤800℃ and periodical decrease at T≥850℃. In the temperature range 850-875℃ the oxidation ability together with rate constant value decreases. X-raylayer-by-layer phase and metallographic analyses of a scale formed over a Ni{sub}3Ta surface during oxidation was carried out. The scale consists of NiO, NiOTa{sub}2O{sub}5, Ta{sub}2O5 as well as Ni and solid solution Ni(Ta). The phase components aredistributed through the layers as follows I (NiO), II (NiO+NiO.Ta{sub}2O{sub}5), HI (NiO.Ta{sub}2O{sub}5+Ni+Ta{sub}2O{sub}5), IV (Ta{sub}2O{sub}5+Ni(Ta)). No NiOTa{sub}2O{sub}5 and Ni(Ta) were found in the scale at low temperatures and short exposures. It is supposed, that change of the oxidation mechanism occurs. The change of properties of the Ta{sub}2O{sub}5 determines diffusion rates of oxygen in the scale of Ni{sub}3Ta.