High-temperature EDS and EBSD Analysis – Enabling In Situ Heating for Direct Observation of Phase Transformations in the SEM

In situ experiments in the scanning electron microscope (SEM) give the capability to perform heating and mechanical testing inside the chamber using dedicated heating and tensile stages. It helps the understanding of a range of phenomena from precipitation and phase transformations to diffusion and segregation in a large range of materials like metals, alloys, ceramics, and composites. It allows metallurgists and material scientists to develop new materials with better properties and make best use of new manufacturing techniques such as 3D printing. Energy Dispersive Spectrometry (EDS) is the routine technique in SEM to analyze elemental distribution and composition within a sample. Electron Backscatter Diffraction (EBSD) is the routine technique in SEM to analyze crystallographic and structural differences within a sample. Combining EDS and EBSD provides a more comprehensive dataset and more information about the sample, however challenges related to high temperature experiments need to be resolved in order for the analysis to be compatible with heating experiments. High-temperature experiments in the SEM on bulk samples can be challenging due to the excess IR radiation that's emitted from the sample and the heating elements on the stage. Shielding on the stage has an influence, however the intensity of the IR signal will cause problems for normal EDS and EBSD analysis. EBSD has been used in combination with in situ experiments for several years, however the solutions have often resulted in a reduced performance of the EBSD system, and the setup resulted in compromises compared to room temperature analysis. In addition, EDS performance at high temperature in the SEM can be severely degraded due to the emission of visible light and IR radiation. In this work we describe recently developed solutions that enable high-temperature EDS and EBSD analysis in the SEM and the direct observation of dynamic chemical changes. We show a dedicated in situ testing system that has been developed, in collaboration with TESCAN, NewTec, and Oxford Instruments, at the University of Manchester. The system is fully automated, enabling long-duration heating and/or testing experiments to be performed without manual attendance. The system can image and characterize large areas of the sample at every step and includes dedicated EBSD and EDS detectors that have been optimized for performance at high temperatures (using novel IR filtering technologies). The example in Fig. 1 shows a combined high-temperature experiment in a Fe-Ti alloy. The data were collected using a TESCAN Clara SEM, Oxford Instruments AZtecLive software, Ultim Max EDS detector and Symmetry S3 EBSD detector. The sample was heated to 900°C and then cooled to 500°C using the NewTec heating stage and automation software. The experiment allowed the direct observation of Fe diffusing in the matrix and then Ti phase transformation from the alpha to beta phase. Using these new solutions, in situ heating experiments combined with EDS and EBSD are now achievable without compromise in data quality or significant risk of damage to the detector hardware. Showing EBSD orientation map, EBSD phase map, combined EBSD band contrast and EDS element map acquired from Ti-Fe alloy sample at 730°C.