Effect of a high hafnium content on the high temperature oxidation of chromium-rich cast alloys. Part 4: Isothermal oxidation and scale spallation of Ni-based alloys

Author(s): Elodie Conrath, Patrice Berthod

The chromium-rich nickel-based alloys without hafnium or with high contents in Hf, previously studied in oxidation during their heating up to 1000°C and 1100°C, were here first characterized in 46 hours-long isothermal oxidation at these temperatures. Second, the cooling parts of the thermogravimetry curves were also exploited, to specify their resistance against oxide spallation. The totalmass gains achieved during the isothermal stages were logically higher for a higher temperature, and slightly lower in presence of hafnium for less than 5wt.% of this element. Beyond this limit the oxidation ratemay become higher than in absence of hafnium. Concerning the resistance against oxide spallation during cooling the beneficial effect of hafnium, well known for much lower Hf contents, still exists with the Hf contents considered in this work. Chromium-rich nickel-based alloys containing so high Hf contents, for example destined to reinforcement by HfC carbides, still present good behaviour in oxidation at high temperatures, with additionally improvement for notably oxide scale spallation.

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