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1

Iron Aluminides and Petr Kratochvíl

100%

Paidar V.

Acta Physica Polonica A

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2015

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vol. 128

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issue 4

467-469

EN

Professor Petr Kratochvíl initiated a modern investigation of this class of materials in our country. He has been interested in various methods how to improve iron aluminides by alloying, precipitation and insertion of hard particles. He also restored the results obtained already in fifties of the last century in the development of so called PyroFerAl that was produced in Czechoslovakia and used, for example, for heat treatment installations. Professor Petr Kratochvíl has been cooperating with leading institutions for material research, for instance, with the Institute of Physics of Materials AS CR in Brno on creep studies or with the Technical University in Ostrava on material formation processes. Since aluminium is near the nonmetals on the periodic table, it can bond with metals differently than do other metals and hence the properties of iron aluminides, in particular, are different from the other intermetallics. These alloys can be also used as functional materials due to their magnetic properties. Iron aluminides are being developed for use as structural materials and/or cladding alloys in fossil energy systems. They have good high temperature mechanical properties and excellent corrosion resistance. These alloys offer relatively low material cost, conservation of strategic elements and a lower density than stainless steels, and thus they have a great potential for substituting steels at elevated temperatures. However, a wider use of these materials is partly hampered by their moderate ductility at ambient temperatures.

2

Displacive Phase Transformations and Generalized Stacking Faults

51%

Paidar V., Ostapovets A., Hardouin Duparc O., Khalfallah O.

Acta Physica Polonica A

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2012

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vol. 122

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issue 3

490-492

EN

The displacive phase transformations can be considered as composed of two processes, namely, pure displacements, shuffling or shearing of atomic planes, and supplementary homogeneous lattice deformation changing also the dimensions of the moving planes. Such deformation causes shape memory effect when the structural transformation is reversed. General displacements of atomic planes will be examined, i.e. γ-surface type calculations will be reported for single plane shuffling, alternate shuffling of every other bcc atomic plane and successive displacements of parallel atomic planes producing in combination with homogeneous deformation the close packed structures. The results of calculations using the many-body potentials of the Finnis-Sinclair type will be compared with ab initio calculations that indicate in which way the phase transformation can be initiated.

3

Topological Model of Austenite-Martensite Interfaces in Cu-Al-Ni Alloy

51%

Ostapovets A., Zarubova N., Paidar V.

Acta Physica Polonica A

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2012

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vol. 122

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issue 3

493-496

EN

Discussion of the austenite-single-variant martensite interfaces in Cu-Al-Ni alloy is performed in the frame of a topological model of martensite interfaces. This model takes into account admissible defects lying in the interface. The results are compared with the experimental data obtained on the foils of Cu-Al-Ni alloys deformed in situ in a transmission electron microscope.

4

What Types of Stacking Faults and Dislocation Dissociations Can Be Found in Transition-Metal Disilicides

51%

Paidar V., Čák M., Šob M., Inui H.

Acta Physica Polonica A

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2015

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vol. 128

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issue 4

589-591

EN

Identical atomic planes of transition-metal disilicides can form different stacking when they are ordered in several combinations of four different positions A, B, C, D. The following arrangements can be formed: AB in C11_b structure of e.g. MoSi₂, ABC in C40 structure of e.g. VSi₂ and ABDC in C54 structure of e.g. TiSi₂ disilicides. The ABC atomic plane stacking along the ⟨111⟩ cubic directions is well known in the fcc lattice, where three basic types of stacking faults are known: intrinsic or extrinsic faults and elementary twin, however, other types of stacking faults can be detected in transition-metal disilicides due to the occurrence of the fourth position D. On the other hand, the faults well known in metallic systems as antiphase boundaries need not be metastable in disilicides. Based on the results of ab initio calculations, it can be predicted which types of planar defects are metastable corresponding to the local minima on the energy surface of generalized stacking faults or unstable when they are represented, for example, by saddle points. The character of dissociation of the dislocation cores is directly related to the existence of metastable stacking faults. Moreover, the space distribution of dislocation cores has a direct impact on dislocation mobility and, therefore, also on macroscopic mechanical properties of materials. The behaviour of extended crystal defects in disilicides that is caused by covalent interatomic bonding, is discussed starting from the geometrical analysis, and it is demonstrated that predictions of materials properties can be deduced.

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4 Acta Physica Polonica A

2 2015

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1 Khalfallah O.

1 Zarubova N.

1 Čák M.

1 Šob M.

Iron Aluminides and Petr Kratochvíl

Displacive Phase Transformations and Generalized Stacking Faults

Topological Model of Austenite-Martensite Interfaces in Cu-Al-Ni Alloy

What Types of Stacking Faults and Dislocation Dissociations Can Be Found in Transition-Metal Disilicides