Chemistry, Bonding and Mechanical Properties of Grain Boundaries in Intermetallic Compounds

Abstract

Grain boundaries in ordered intermetallic compounds have a great influence on their mechanical properties. Considerable progress has been made on characterizing the chemistry at grain boundaries experimentally and understanding their electronic structure theoretically. The approach in the present study is to experimentally examine the bonding changes at grain boundaries, in the presence and absence of dopants, using Electron Energy Loss Spectroscopy (EELS), and interpret these changes in terms of the observed mechanical properties.EELS of transmitted electrons probes excitations which occur at unique energy losses. In the present study, the Ni L2,3 edges were examined which select excitations from the Ni 2p orbitals to states above the Fermi level. For single electron excitations, it can be shown that the area under the sharp peaks at the onset of the L2,3 edges is proportional to the number of holes in the Ni d band for the 3 d transition metals. Fig. 1 shows the EELS spectra from bulk Ni, Ni3Al and Ni3Si. The edge intensity (historically called a white line) is reduced in Ni3Si and Ni3Al with respect to Ni.