The aerospace industry has a need for new metallic alloys that
are lightweight and have high strength at elevated temperatures.
However, the current design method for new materials is largely
experimental, requiring substantial capital investment in processing
the material and in determining the material's microstructure
and properties. Theoretical methods that would narrow the field
of promising candidate materials could substantially reduce cost
and development time.
The BFS (Bozzolo, Ferrante, and Smith) method is a new, computationally
efficient and physically sound quantum semi-perturbative approach
for describing metals and their defects. Based on a simple interpretation
of the alloy formation process that identifies strain and chemical
contributions to the energy of the alloy, the method provides
an atom-by-atom description of an alloy. Its implementation requires
little more than algebra and the solution of transcendental equations.
In contrast, methods previous to BFS suffered from many limitations.
The state-of-the-art nonatomistic approaches rely heavily on developing
a substantial data base, then extrapolating to predict new properties.
Although this approach has been successful, it leads to incremental
rather than revolutionary improvements. Other approaches--such
as first-principles, quantum mechanical methods, and other competing
semi-empirical methods--suffer from more serious limitations.
Quantum mechanical methods, although in principle the best, require
so much CPU time as to make calculations on applied problems infeasible.
Competing semi-empirical methods are limited to a few face-centered-cubic
metals and are not successful in predicting most alloy properties.
At the NASA Lewis Research Center, we have demonstrated (ref.
1) that BFS can investigate the properties of a large number of
alloys with a minimum computational effort on low-level computers.
This screening allows the selection of the best alloy candidates
for a particular application and, therefore, promises large cost
savings over current approaches.
BFS has been tested in a variety of situations, consistently giving
results in excellent agreement with experimental results. More
recently, the method has been optimized for modeling ordered intermetallic
alloys that are of interest in aeronautical applications, including
the determination of the defect structure of FeAl alloys (ref.
2) and the characterization of ternary and quaternary Ni3Al-based
alloys (ref. 3). Much of the recent effort, however, has focused
on alloy design of NiAl-based materials. The complexity of the
systems modeled range from three-component, two-phase alloys (such
as the Ni-Al-Ti alloys shown in the first figure) to five-component,
three-phase alloys that exhibit solute enrichment at the interfaces
(as shown in the following figure). Such complex structures cannot
be modeled by alternative techniques, and the accuracy of the
predictions has been verified by appropriate experimental studies.
The BFS method is not limited solely to high-temperature structural
alloy design. It can be applied to the design of high-performance
alloys for any application. In addition to the design function,
it can be used in place of or in conjunction with experiments
to analyze the poorly understood mechanical and thermal properties
of existing alloys. The method also has shown potential to perform
revolutionary analysis of alloy structures and thin films and
to be applied in interface-related studies (ref. 4).
Previous articleLast updated April 30, 1997
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