The origin of the superior high temperature strength of Ti-rich gamma-TiAl with addition of Nb is a highly controversial issue. In this paper, we calculated the interaction energies between point defects in these alloys using a first-principles plane-wave pseudopotential method. It is found that, the nearest neighbouring Nb atoms on Al-sublattice (Nb(Al)) repel whereas the next nearest neighbouring Nb(Al) atoms attract each other, indicating that Nb(Al) atoms may form short-range ordered structure. Based on this finding, we propose that the short-range order may be responsible for the high strength of the Ti-rich TiAl-Nb alloys. (C) 2010 Elsevier Ltd. All rights reserved.
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