Calculations of Cu L2,3 fine structure at grain boundaries

Abstract

The segregation of impurities to grain boundaries in metals and alloys has been known for some time to make changes in ductility. Examples of this effect are the embrittlement of copper by the addition of bismuth and the ductilization of Ni3Al by boron impurities. The mechanism by which these dramatic changes in mechanical properties arise is still largely unknown. It has been suggested that embrittling elements draw charge from neighbouring metal atoms while impurities that enhance ductilty act in the opposite way. Changes in the electronic states can be detected as changes in the energy loss spectrum when a small probe in a FEG STEM is moved across the boundary. Recent work by Muller has shown significant differences between the Ni L3 spectrum from grain boundaries in Ni3Al with and without boron. Bruley has shown that a “white line”, indicative of empty Cu d states, appears in the Cu L3 edge from Cu atoms near boundaries where bismuth has segregated.