Corrosion Behaviour of Inconel 617 Coated with Silicon Oxides in Impure Helium

Abstract

Inconel 617 samples were coated with silicon or silicon oxide SiO_X(0<X≤2) films by reactive magnetron sputtering method. The coated samples were corrosion-tested in an impure helium environment at 900 and 1 000°C. The impure helium simulates the coolant gas of a high temperature gas cooled reacter now being developed in Japan. The SiO_X(X<2) films reacted with the substrate alloy, Inconel 617 at elevated temperatures. Silicon in the SiO_X films diffused into the substrate to form the carbide of (Si, Mo)_X C_Y. Nickel and Chromium in the substrate diffused into the SiO_X films to form silicides. The SiO_X(X<2) films exfoliated appreciably during the corrosion test and hardly protected the substrate against corrosive attack by the impure helium. Rather, SiO_X(X<2) films enhanced a carburization of Inconel 617 in the impure helium.
On the other hand, the stoichiometric SiO₂ films had an excellelent protective effect in the impure helium at 900 and 1 000°C. However, the protective effect of the SiO₂ film degraded a little at 1 000°C. Inconel 617 was carburized and oxidized internally to form aluminum internal oxide-layer at 1 000°C.