High temperature oxidation and glass corrosion of cobalt base superalloys

Metallic materials used in the hottest parts of glass making machines are exposed to mechanical deformation, oxidation by different gases and hot corrosion by molten glass. Here the oxidation and corrosion behaviour of cobalt base superalloys are studied. The use of both thermogravimetry and electrochemical techniques allows a good and quantified knowledge about these properties. After a wide characterization of two reference alloys, this work focused on the influence of several parameters, which belong to either the chemical and microstructural ones or to the process ones. It has been done with the elaboration and the study of other alloys which differ from the references on the carbon, tantalum or tungsten contents, and by varying the time/temperature preoxidation couple or the glass/alloy relative movement. For example, it appeared that high contents of carbon or heavy elements lead to a faster oxidation, and all alloys can get a passive state if preoxidised during a sufficient time that depends on the temperature.