Ab-initio Modeling of the Local Short Range Order in Titanium-, Zirconium-based Alloys and High Entropy Intermetallics
“Ab-initio Modeling of the Local Short Range Order in Titanium-, Zirconium-based Alloys and High Entropy Intermetallics”
Dr. Yu. Matviychuk
G.V. Kurdyumov Institute for Metal Physics,
National Academy of Sciences of Ukraine, Kiev
December 18, 2018 (10.00 - 10.45)
Graduiertenschule MUSiC, Appelstr. 11A
Seminar room A 501, 5st floor
The aim of this presentation is to show the possibilities that might arise from computer modeling of the electronic and crystal structure of the modern structural and functional metallic materials. Below, three particular cases illustrate those possibilities.
The results of the computer ab-initio modeling of the atomic structure and physical properties of Me-Nb (Me=Ti, Zr) ß-alloys are going to be presented. Single phase β-alloys were modeled as a set of Me 54-m Nbm (m=2,4,8,10,12,14) superstructures with the 3 х 3 х 3 unit cell size. To calculate elastic constants and Young`s moduli at elastic and isotropic material approximation the high precision "ab-initio" FLAPW method was used. Comparison of the results obtained with experimental data has been carried out. It was shown that partial substitution of titanium by zirconium in Ti1-xNbx alloy leads to the decrease of Nb concentration that correspond to single phase ternary alloy with decreasing elastic moduli. At certain concentrations the results of the calculations allow to predict significant decrease in Young`s moduli (Е001) in ternary alloys comparing with binary ones, which is important for medical applications of these materials.
The results of the modeling of the electronic and crystal structure of ZrMe (Me=Cu, Ni,Co) intermetallics, which might be considered as a basis of high temperature shape memory alloys, have been presented also. The total energy of the ordered B2 crystal structure, modeling ZrCu austenite, decreases at the lowering of the lattice symmetry - formation of B19` and Cm martensitic phases. The origin of the model ZrCu austenitic phase instability and of the B19` and Cm martensite model phase formation is in the possibility of the two types of short range order existence in ZrCu: first short range order type is determined by Cu-Zr interatomic interaction, while the second by Cu-Cu one. Refined atomic coordinates in the unit cells for both marten sites allow us to confirm the presence of two short range order types in the real B19` and Cm martensitic crystals.
Recent modeling results of the atomic structure of high entropy TiZrHfCoNiCu high entropy shape memory alloy will be also shown. It has been found that the interatomic bond lengths are essentially different from what can be seen in ideal B2 type structure. As a result, atomic positions are significantly shifted from their ideal positions. It has been shown that the origin of such strong distortions of the Ti9Zr9Hf9Co9Ni9Cu9 crystal lattice lays in the strong interatomic interaction of Ti atoms with Co and Ni. Essential characteristic feature of such interactions is much smaller bond length of Ti-B (B = Co, Ni) comparing with bond lengths Zr - B and Hf - B.