The Role of Computational Modeling Processes in the Development and Understanding of NiAl-Based Ordered Intermetallic Al
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*Ohio Aerospace Institute, 22800 Cedar Point Road, Cleveland, Ohio 44142. "**NationalAeronautics and Space Administration, Lewis Research Center, Cleveland, OH 44135
ABSTRACT A detailed understanding of the structure of ordered intermetallic systems is difficult at best, causing a serious disconnect in the typical process-structure-properties approach to alloy development. Basic information, like the site substitution schemes of various alloying elements, partitioning behavior in multiphase alloys, and the dependence of these phenomena with concentration and higher order alloying additions is necessary to predict and understand the effect of various alloying schemes on the physical and mechanical properties of a material. It is only recently that theoretical methods can begin to provide useful insight in these areas, as most current techniques suffer from strong limitations including the type and number of elements that can be considered and the crystallographic structure of the resulting phases. The Bozzolo-Ferrante-Smith (BFS) method for alloys was designed to overcome these limitations, with the intent of providing a useful tool for the theoretical prediction of fundamental properties and the structure of multi-component systems. The role or potential contributions of theoretical procedures like the BFS method to the alloy design process are discussed with a specific emphasis on work that has been conducted on NiAl-based alloys. After a brief description of the method and its range of applications, we will concentrate on the usefulness of BFS as an alloy design tool. The theoretical determination of site substitution schemes for individual as well as collective alloying additions to NiAl, the resulting behavior with respect to solubility limits and second phase formation, and the concentration dependence of the lattice parameter will be demonstrated.
INTRODUCTION The calculation of the energetics of an arbitrary alloy system has proven to be a difficult but unavoidable task. Especially if substantial progress in a theoretical (non-empirical) approach to alloy design is to ever become a reality. First-principles calculations have been successful in handling binary and a few ternary systems, providing detailed information on essential features. However, examination of practical engineering materials would require the analysis of systems with at least three, and in the case of some materials like superalloys, 10 or more elements, with the complication of second phases and an occasional need to determine interfacial and surface properties. These types of 'real-world' problems are beyond the computational ability of first principles techniques. But recent development of powerful semiempirical methods, designed to efficiently deal with large and complex systems, greatly enhances the possibility that such techniques will some day be commonly used in alloy design and analysis. Recently, Bozzolo, Ferrante and Smith (BFS) introduced such a method [1], with a sound physical foundation and minimum need for parameterizatio
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