Ellingham diagram: A new look at an old tool

Abstract

Ellingham diagrams are thermodynamic tools that allow comparing the relative stability among oxides. They are well established for pure metals, but they can be obtained for any multi-element system if the chemical activity of each component is known. However, chemical activities are very difficult to obtain experimentally and, because of the lack of these data, Ellingham diagrams have never been reported for complex industrial alloys. This work aims to show how nowadays advanced thermodynamic databases can be used to supply for this lack. Herein, the Ellingham diagrams of four wildly used alloys- TiAl 48–2–2, TA6V, Inconel 718 and 304 steel- have been computed. The results are discussed in respect to the oxidation behavior of these alloys and important differences in respect to the Ellingham diagram of pure metals are highlighted.