Ab initio simulation of a tensile test in MoSi 2 and WSi 2
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Ab initio simulation of a tensile test in MoSi2 and WSi2
ob, and V. Vitek M. Fri a k , M. S Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Z izkova 22, CZ-61662 Brno, Czech Republic, [email protected] Department of Solid State Physics, Faculty of Science, Masaryk University, Kotlarska 2, CZ-61137 Brno, Czech Republic Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6272, U. S. A. y
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ABSTRACT
The tensile test in transition metal disilicides with C11b structure is simulated by electronic structure calculations using full potential linearized augmented plane wave method (FLAPW). Full relaxation of both external and internal parameters is performed. The theoretical tensile strength of MoSi2 and WSi2 for [001] loading is determined and compared with those of other materials. ab
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INTRODUCTION
Transition metal (TM) silicides are considered as a very promising basis for a new generation of high-temperature structural materials that can signi cantly improve the thermal eÆciency of energy conversion systems and advanced engines. The reason is that at high temperature they combine the ductility and thermal conductivity of metals with high strength and corrosion resistance of ceramics. Intrinsic oxidation resistance is due to the formation of silicon oxide lms at surfaces and high creep strength is related to low di usion coeÆcients. The melting temperature is much higher than that of Ni-based superalloys or Ni and Ti-based aluminides and is comparable to that of silicon-based ceramics. The largest impediment is low ductility and/or toughness at ambient temperatures. The purpose of this paper is to investigate, from rst principles, the electronic structure and ground state of TM-disilicides, MoSi2 and WSi2, with C11b structure, to simulate a tensile test for ideal crystal without defects, including full relaxation of both external and internal parameters, and to determine thus the theoretical tensile strength for the [001] loading. TENSILE TEST SIMULATION
The tensile strength of materials is usually limited by presence of internal defects, mostly dislocations. In a defect-free crystal, the tensile strength is several order of magnitude higher and is comparable with elastic moduli. Most of the calculations of theoretical (ideal) strength is based on empirical potentials with the parameters adjusted to experimental data. However, most of these experimental data correspond to the equilibrium ground state. Therefore, the N4.8.1
2 semiempirical approaches adapted to the equilibrium state may not be valid for materials loaded close to their theoretical strength limits. In the rst-principles ( ) electronic structure calculations, we start from the fundamental quantum theory. The only input is atomic numbers of the constituent atoms and, usually, some structural information. This approach is reliable even for highly nonequilibrium states. To simulate the tensile test, we rst calculate the total energy of t
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