Energy-filtered electron microscopy study on phase transformation of alloys

Recent progress of electron microscopy on phase transformations of alloys, especially energy-filtered electron microscopy, was reviewed mainly on the basis of the recent works by the authors. In the energy-filtered electron diffraction patterns of both Cu72.5Pd27.5 and Ti50Ni48Fe2 alloys, weak diffuse scattering which resulted from the diffusional and displacive phase transformations, respectively, was clearly observed by virtue of the background subtraction. In a short-range ordered state of a Cu72.5Pd27.5 alloy, through the careful evaluation of the dynamical diffraction effect on the diffuse scattering, short-range order parameters were evaluated quantitatively. On the other hand, in the premartensitic state of a Ti50Ni48Fe2 alloy, the morphology and growth process of microdomains less than 5 nm with a single transverse type of atomic displacement were clarified by energy-filtered electron diffraction and in situ dark-field electron microscopy. Furthermore, through in situ electron energy-loss spectroscopy on L2,3 core edges of a Ti50Ni48Fe2 alloy, the change in the electronic structure due to the martensitic transformation was analyzed. Thus, it is clearly demonstrated that advanced electron microscopy utilizing electron energy-loss spectroscopy is effective to make clear the change in both crystal and electronic structures associated with phase transformations in alloys.