Abstract
Materials modelling involves research that spans the very broad spectrum of length scales from quantum mechanical calculations at the A level all the way through to finite-element or finite-difference modelling at the continuum level. This paper reviews the role that quantum mechanics plays in the modelling hierarchy with particular reference to the titanium and nickel aluminides.
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A. R. C. Westwood (Sandia National Laboratories,USA). What are the prospects for extending this approach to ternary and quaternary alloys with the ultimate objective of developing, from first principles, an intermetallic that exhibits significant ductility?
D. G. Pettifor. The approach of modelling defects using bond order potential is easily extendable to a treatment of ternary and quaternary alloys provided the appropriate tight binding parameters between the different chemical constituents are known. These calculations at the electronic and atomistic level would have to be linked to simulation of dislocation behaviour at the microstructural level before we have a truly `first principles’ modelling capability of ductile behaviour.
K. S. Kumar (Martin Marietta Laboratories,Baltimore, USA). Given that the mechanical properties of intermetallic compounds are particularly sensitive to mi-nor stoichiometric deviations as well as minor alloying additions, how realistically can we expect atomistic modelling to serve as a predictive tool, since the number of atoms/cells that can be included is limited? Further, can defect population be included in the calculations?
D. G. Pettifor. The sensitivity of planar fault energies to alloying additions is already being modelled. As the interatomic potentials become more realistic and computers ever more powerful, we can expect that modelling will be able to provide new insight into the role of alloying additions and non-stoichiometry on mechanical properties.
R. W. Cahn (University of Cambridge, UK). Professor Pettifor showed, for certain intermetallic phases, that the energy differences between the stable and the next-most-favourable crystal structures are exceedingly small. Can he reliably predict which of such phases will exhibit stacking faults (polytypism), like SiC or Co?
D. G. Pettifor. Yes, even though the absolute energy may show sizeable error, relative energies are usually very reliable. The polytypism in SiC or Co has been successfully predicted by groups in the Cavendish Laboratory and the Techniche Hochschule in Darmstadt.
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Manh, D.N., Bratkovsky, A.M., Pettifor, D.G. (1996). Quantum mechanical predictions in intermetallics modelling. In: Cahn, R.W., Evans, A.G., McLean, M. (eds) High-temperature Structural Materials. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-0589-7_8
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DOI: https://doi.org/10.1007/978-94-011-0589-7_8
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