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Defect Structure of β NiAl Using the BFS Method for Alloys

Published online by Cambridge University Press:  10 February 2011

Guillermo Bozzolo ,
Carlos Amador ,
John Ferrante  and
Ronald D Noebe
Guillermo Bozzolo
Affiliation:
Analex Corporation, 3001 Aerospace Parkway, Brook Park, OH, 44142-1003
Carlos Amador
Affiliation:
Facultad de Qufmica, Universidad Nacional Auténoma de México, Ciudad Universitaria, 04510 Distrito Federal, México.
John Ferrante
Affiliation:
National Aeronautics and Space Administration, Lewis Research Center, Cleveland, OH 44135.
Ronald D Noebe
Affiliation:
National Aeronautics and Space Administration, Lewis Research Center, Cleveland, OH 44135.
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Abstract

The semiempirical BFS method for alloys is generalized by replacing experimental input with firstprinciples results thus allowing for the study of complex systems. In order to examine trends and behavior of a system in the vicinity of a given point of the phase diagram a search procedure based on a sampling of selected configurations is employed. This new approach is applied to the study of the/3 phase of the Ni-Al system, which exists over a range of composition from 45–60 at. % Ni. This methodology results in a straightforward and economical way of reproducing and understanding the basic features of this system. At the stoichiometric composition, NiAl should exist in a perfectly ordered B2 structure. Ni-rich alloys are characterized by antisite point defects (with Ni atoms in the Al sites) with a decrease in lattice parameters. On the Al-rich side of stoichiometry there is a steep decrease in lattice parameter and density with increasing Al content. The presence of vacancies in Ni sites would explain such behavior. Recent X-ray diffraction experiments suggest a richer structure: the evidence, while strongly favoring the presence of vacancies in Ni sites, also suggests the possibility of some vacancies in Al sites in a 3:1 ratio. Moreover, local ordering of vacant sites may be preferred over a random distribution of individual point defects.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 408: Symposium P – Materials Theory, Simulations, and Parallel Algorithms , 1995 , 375
Copyright
Copyright © Materials Research Society 1996

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