Behaviour of 25wt.Cr-containing Fe-based alloys strengthened by hafnium carbides in oxidation between 1000 and 1200°C

摘要

Three alloys based on iron and containing 25 wt.%Cr, 0.25 to 0.50 wt.%C and 3.7 to 5.6 wt.%Hf, candidates for high temperature applications thanks to their high melting points, were synthesized by foundry and tested in oxidation at high temperature (1000 to 1200°C) in air. The mass gains were treated using the {m x dm/dt = Kp – Kv × m} method when applicable and the oxidized samples were subjected to postmortem characterization. The obtained oxidation kinetic was not always regular enough to correctly extract the two constants Kp and Kv (chromia volatilization for T equal to 1100 or 1200°C), but this was possible in some cases. The external oxide was mainly composed of (Cr, Fe)_2O_3 oxide and also contained some HfO_2 islands. Accelerated oxidation seemed starting in some locations of the surface of the 1200°C-oxidized samples, which let think that catastrophic oxidation ought to generalize beyond the 46 hours of these tests. Obviously these alloys need to be enriched in chromium to delay such scenario, or to benefit of a protective coating.