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 d iffraction patterns of both Cu72.5Pd27.5 and Ti50Ni48Fe2 alloys, weak diffu se scattering which resulted from the diffusional and displacive phase tran sformations, respectively, was clearly observed by virtue of the background subtraction. In a short-range ordered state of a CU72.5Pd27.5 alloy, throu gh the careful evaluation of the dynamical diffraction effect on the diffus e scattering, short-range order parameters were evaluated quantitatively. O n the other hand, in the premartensitic state of a Ti50Ni48Fe2 alloy, the m orphology and growth process of microdomains less than 5 nm with a single t ransverse type of atomic displacement were clarified by energy-filtered ele ctron diffraction and in situ dark-field electron microscopy. Furthermore, through in situ electron energy-loss spectroscopy on L-2,L-3 core edges of a Ti50Ni48Fe2 alloy, the change in the electronic structure due to the mart ensitic 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 structur es associated with phase transformations in alloys. (C) 2001 Elsevier Scien ce B.V. All rights reserved.