Degradation at 550°C of cast chromium-rich cobalt-based alloys exposed to a H2O-O2-CO2-HCl gaseous mixture
Résumé
For applications at moderate temperature, even in presence of intense mechanical stresses and very aggressive fluids, alloys which are needed can be ones which may be different from the superalloys used as turbine blades in aeronautics or power generation, and cheaper than them. This is for example the case of high performance stainless steels, nickel alloys, or why not cobalt-based alloys. These alloys may bring interesting mechanical strength and correct resistance against oxidation by gases and corrosion by molten substances. Cobalt alloys have rather found new applications such as hot tools for working molten glass. The oxidative gaseous milieu in which cast cobalt-based superalloys work the most often are dry or wet air, or mixtures of burner gases. However there are applications, notably in the waste-to-energy (WtE) plants, in which hot gases are present as mixtures of many very aggressive chemical substances (in WtE boilers), for which cobalt-based superalloys may be considered. Their behaviour in so highly hostile environment seems to have been never investigated. This is why one decided here to test some cast cobalt-based alloys in hot environments typical of waste valorisation for energy production.
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