In Situ Investigation of the Oxidation of Cobalt-Base Superalloys in the Environmental Scanning Electron Microscope

• Published in: Advanced engineering materials Vol. 17; no. 8; pp. 1158 - 1167
• Main Authors: Weiser, Martin, Reichmann, Angelika, Albu, Mihaela, Virtanen, Sannakaisa, Poelt, Peter
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.08.2015
• Subjects: Chambers; Cobalt base alloys; Crystallites; Crystallography; Grain boundaries; Orientation; Oxidation; Scanning electron microscopy; Superalloys
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.201500146

Since their discovery in 2006, cobalt‐base superalloys have aroused increasing interest as potential materials for various high‐temperature applications. One of the still unsolved problems is their resistance to oxidation. In the present study, the very first stages of the oxidation process of a Co–9Al–9W alloy were investigated. To this aim, the progress of the oxidation process was continuously observed at high magnification in an environmental scanning electron microscope (ESEM). Oxidation starts not necessarily at the grain boundaries, and both the onset temperature and the oxidation rate depend on the crystallographic orientation of the crystallites. A heating stage mounted in the specimen chamber of an environmental scanning electron microscope (Figure) enables the continuous observation of the development of the corrosive structures during hot corrosion experiments. The temperature, at which the oxidation of the material starts, can be determined, and the dependence of the corrosion process on the crystallographic orientation of individual grains can be observed.