EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

MAX phases are a highly anisotropic material, giving rise to a large variation in their properties depending on orientation of the crystal lattice. Typically, orientation can be determined through Electron Backscatter Diffraction (EBSD), is a powerful technique with very high spatial resolution and the ability to determine strain in a crystal structure. However, it requires a high level of sample finish, long scan times and can be limited but sample size dependant on the machine used. Raman spectroscopy is highly sensitive to the anisotropic nature of the MAX phases, leading to significant changes to full width half maximums and intensities of peaks. Raman has a lower spatial resolution ( ~700 nm), but requires essentially no sample preparation and allows for rapid acquisition of data in comparison to EBSD. Therefore, we have been able to correlate orientations provided by EBSD to Raman spectra taken in those grains, allowing for rapid orientation analysis of samples.

As Raman is sensitive to changes in bond length, it can analyse strain at the bonding level, as any change in bond length will lead to a shift in the Raman peak. This makes it an incredibly powerful technique for MAX phases as peaks relating to the M-A and M-X are segregated into two different regions of the Raman spectra. This means it is possible to determine how strain is being accumulated in the different layers of the MAX phase. As each peak shows a specific shift, dependant on orientation and loading orientation, correlating to a specific strain. Therefore, we can determine the extent of the non-homogeneous deformation of the MAX phase lattice through Raman spectroscopy.