An investigation into experimental in situ scanning electron microscope (SEM) imaging at high temperature.

This paper presents an investigation into high temperature imaging of metals through the use of a novel heat stage for in situ Scanning Electron Microscopy (SEM). The results obtained demonstrate the benefits and challenges of SEM imaging at elevated temperatures of up to 850 °C using Secondary Electron (SE) and Electron Backscatter Diffraction (EBSD) detectors. The data collected using the heat stage demonstrate good beam, vacuum, and detector stability at high temperatures without the need for shielding or detector modification owing to the heat stage geometry. SE imaging highlighted one possible application: carrying out thermal etching, a process in which surface grooves form along a material's grain boundaries during heating in situ. The data suggest that using the heat stage to perform imaging during the process gives a more accurate representation of a material's microstructure at temperature than examining the thermally etched specimen after cooling. This study also highlights some of the challenges of high temperature in situ EBSD imaging in both steel and nickel at a variety of temperatures and time scales. In particular, the data demonstrate the effect of surface roughness on EBSD imaging and how microstructural changes during heating may affect this. Additionally, the ease with which a material can be imaged using EBSD at temperature may be affected by the material's magnetic properties. For the first time, it is shown that at temperatures close to the Curie temperature of ferromagnetic materials, in this case Nickel, there is a loss of EBSD image quality. Quality was regained when temperatures were further increased. Despite these challenges, good quality EBSD scans were produced, further highlighting the benefits of in situ testing for providing information on grain boundaries, orientations, and phase change at elevated temperatures.