The shape memory alloys (SMAs) have been used since 1971. The main attention turned from the first applied alloy Nitinol to copper-based alloys, but the second half of 80’s returned the leading position in the field to Nitinol as a stent implants material. The significant boost for SMAs was the discovery of the magnetically induced martensitic transformation in Ni2MnGa based alloys. Nevertheless, the field of SMA is much wider and contain various, even peculiar, alloys connected just by presence of the martensitic transformation - diffusionless transformation, where atoms moves just the distances shorter than lattice parameter. Compared to usual habit of metals, the response to mechanical stress (or other external force) in SMAs is not standard, and there should be an explanation, why the deformation is not proceeded via creation of dislocations. The processes behind such behavior are usually the long distance forces of precipitates and the high or specific density of the planar defects in lattice.
In the presented paper we overview of the fruitful exploration of the electron back-scattered diffraction (EBSD) method to investigate the solid state phase transformations in SMAs. EBSD method, as the improvement and evaluation of observed Kikuchi lines, is even older than electron microscopy itself and dates back to 1928. It allows us to establish the orientation of the known lattice in the point illuminated by the electron beam. Presented results cover the wide range of SMAs.
The transformation in Co-Ni-Al alloys is the example of the stress induced martensitic transformation stabilized by the particles of the non-transforming phase. The real martensitic variants were distinguished from polishing artefacts having the same shape as these variants by EBSD.
The extremely similar variants of very slightly monoclinic martensitic phases in Ni-Mn-Ga alloys can be distinguished by EBSD too, although some differences are below the resolution limits of the method and evaluation must be improved by manual evaluation or additional presumptions. The more known SMA alloys in the same category represents NiTi being functionalized by precipitates and copper based alloys as Cu-Al-Ni driven by a cascade of martensitic transformations and their twinning boundaries.