Abstracto

Oxide spallation during cooling from high temperatures affecting carbides-containing nickel-based alloys. Part 1: Case of ternary Ni-Cr-C alloys with various carbides fractions

Patrice Berthod, Lionel Aranda, Pierric Lemoine

When an alloy preliminarily exposed to high temperature in an oxidizing atmosphere is cooled, its external oxide protective scale can be more or less lost, depending on the thickness of the oxide and on the characteristics of the alloy. This spallation phenomenon was here studied for Ni-30wt.%Crbased alloys containing various amounts in carbon, by exploiting the mass variations recorded in the cooling parts of thermogravimetry curves. It was seen that chromia spallation tends to be more severe, in terms of cooling before start, mass loss rate and final fraction of oxide loss, when the temperature of previous isothermal oxidation is higher and when the carbides fraction in the alloyÂ’s microstructure is lower. This highlights probable effects of the quantity of oxide formed before cooling and of the thermal contraction of the alloy.