Abstract

In this work, an alloy based on nickel, rich in chromium and designed to be reinforced by MC carbides thanks to the presence of 4wt.% Ta and 2wt.% Hf, was elaborated by conventional casting and exposed to air at three temperatures ranging from 1100 to 1250°C, with follow up of the mass changes due to oxidation. The as–cast microstructure is composed of a dendritic matrix and of eutectic carbides of two types. The major type is (Ta,Hf)C carbide and a minor type is chromium carbide. The isothermal mass gains are slow and their kinetics are of a parabolic type at all temperatures. The alloy demonstrated a chromia–forming behavior in all cases, with the development of an external continuous chromia scale and an internal layer of complex oxide Cr(Ta,Hf)O4. The stability of the external scale during cooling was dependent on the quantity of oxides isothermally formed, i.e. on the oxidation temperature for a given duration. The behavior of the alloy in isothermal oxidation at the considered temperatures is satisfactory but solutions must be found for improving the resistance against cyclic oxidation for the highest temperatures.

Keywords

Nickel-based alloy, Hf-doping, Thermal analysis, High temperature oxidation, Metallographic characterization,

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