Electronic Structure and Mechanical Properties of Intermetallics: Apb Energies in Ni-Al-Based Systems

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Abstract
The possible origin of the high degree of brittleness (i.e., low ductility) of the Ni-Al-based alloys in the B2 structures is investigated by means of all-electron self-consistent total energy LMTO calculations. Using a supercell approach, the energetics of the two simplest anti-phase boundaries (APB) for NiAl in the B2 structure - namely the ½ on {110} and ½ on {112} - are calculated for the first time assuming no relaxation at the interface. We find APB energies of order of 800 ergs/cm2 for both cases. Since the calculated APB energies are very high, slip is hardly likely to occur - as suggested experimentally. By substituting Ni or Al with V, Cr or Mn at the APB interface plane, remarkably decreased APB energies are obtained. These first results on these simplified model systems may suggest a way to decrease the APB energy contribution to the ductility of NiAl-based alloys.

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