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Vaclav Vitek Professor 218 LRSM 215.898.7883 vitek@seas.upenn.edu |
Ph.D., Physics, Czechoslovak Academy of Sciences, 1966.
B.S., Physics, Charles University, Prague, 1962.
Research Interests
Theory and atomic level computer modeling of the structure and properties of materials: atomic and electronic structure of interfaces and dislocations. Atomic and mesoscopic level processes of plastic deformation and fracture and link to solid mechanics: multiscale modeling. Deformation and fracture of complex intermetallic compounds.
Current Research Topics
Atomic level behavior of dislocations in transition metals and intermetallic
compounds:
Dislocation core structures control the main characteristics of the plastic
flow in many crystalline materials, ranging from bcc transition metals, such
as molybdenum and tantalum, to complex intermetallics, for example transition
metals silicides. Common signatures of core effects are ‘strange’ slip geometries,
strong and unusual dependence of flow stress on crystal orientation and temperature
and dependence of slip on components of stress other than the shear stress
in the slip direction. In this research we seek the relationship between the
atomic configuration of dislocation cores and macroscopic plastic flow via
computer simulation of the dislocation motion under variously applied stresses.
Using the results of atomistic studies we develop physically based constitutive
models for macroscopic analyses of the plastic flow. Such multiscale modeling
links the atomic level properties of dislocations with macroscopic plastic
behavior and builds a bridge between basic physics and properties of engineering
materials.
Interfaces and grain boundaries:
Many outstanding problems in materials science are closely linked with interfacial
phenomena and the key to a fundamental understanding of the role of interfaces
is their atomic structure. Using computer simulation, we are investigating
the atomic and electronic structure as well as properties such as interfacial
cohesion, diffusion, formation of unusual interfacial phases, interaction
with dislocations and interfacial chemistry related to segregation. The calculations
range from ab initio DFT based electronic structure calculations, real space
tight-binding methods, to state of the art empirical approaches allowing modeling
of very large systems. Examples are studies of Nb/sapphire interfaces and
interfaces encountered in the lamellar TiAl alloys. The modeling is synergistically
linked with the high resolution electron microscopy and other experimental
studies.
Descriptions of atomic interactions for atomistic computer modeling:
The necessary precursor of any atomistic studies is a physically based description
of atomic interactions that reflects correctly the principal aspects of bonding.
We are advancing such descriptions on several levels, ranging from many-body
central-force potentials to bond-order potentials that are capable to reflect
correctly the mixture of metallic and covalent bonding encountered in many
complex structural and functional materials. All these methods are semiempirical
but the principal input into these schemes is from ab initio DFT based calculations,
which are the present state of the art theoretical tool for study of bonding
in materials.
Selected Publications
“Stacking Fault-Type Interfaces and their Role in Deformation,” V. Paidar and V. Vitek, in Intermetallic Compounds - Principles and Practice, Vol. 3, edited by J. H. Westbrook and R. L. Fleisher, John Wiley, New York, p. 437 (2002)
“Bond-order potential for molybdenum: Application to dislocation behaviour,” M. Mrovec, D. Nguyen-Manh, D. G. Pettifor and V. Vitek, Phys. Rev. B 69, 094115 (2004)
“Core structure of dislocations in body-centred cubic metals: relation to symmetry and interatomic bonding,” V. Vitek, Philos. Mag. 84, 415 (2004)
“Dislocations in materials with mixed covalent and metallic bonding,” D. Nguyen-Manh, M. J. Cawkwell, R. Gröger, M. Mrovec, R. Porizek, D. G. Pettifor and V. Vitek, Mat. Sci. Eng. A, 400-401, 68 (2005)
“Origin of Brittle Cleavage in Iridium,” M. J. Cawkwell, D. Nguyen-Manh, C. Woodward, D. G. Pettifor and V. Vitek, Science 309, 1059-62 (2005)
“Construction, assessment, and application of a bond-order potential for iridium,” M. J. Cawkwell, D. Nguyen-Manh, D. G. Pettifor and V. Vitek, Phys. Rev. B. 74, 064104 (2006)
“Atomistic study of athermal cross-slip and its impact on the mechanical properties of iridium,” M. J. Cawkwell, C. Woodward, D. Nguyen-Manh, D. G. Pettifor and V. Vitek, Acta Materialia 55, 161-169 (2007)
“Atom-Based Bond-Order Potentials for Modeling Mechanical Properties of Metals,” M. Aoki, D. Nguyen-Manh, D. G. Pettifor and V. Vitek, Prog. Mater. Science: A Festschrift to honor Prof. D. G. Pettifor, 52, 154-195 (2007)
“Bond screening: a challenge for modelling of intermetallics and fusion materials,” D. Nguyen-Manh, V. Vitek and A.P. Horsfield, Prog. Mater. Science: A Festschrift to honor Prof. D. G. Pettifor, 52, 255-298 (2007)