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 Cu_72.5Pd_27.5 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 Cu_72.5Pd_27.5 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 L_2.3 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.