Thesis (M.Sc. (Physics)) -- University of Limpopo, 2021 / The ab initio density functional theory and molecular dynamics approach have been
used to study the properties of Zr-based systems. In particular Zr-Nb, Zr-Nb-X (X =
Co and Sn). We have calculated the structural, elastic, mechanical properties and
temperature dependence particularly to determine their stabilities. These alloys are
important for a wide range of technological applications, primarily in the nuclear and
chemical industries due to their good irradiation stability, wear and corrosion
resistance, high mechanical strength and superior neutron economy.
The virtual crystal approximation was used to introduce small amounts of either Co
or Sn contents on Zr-Nb system. The main idea is to advance high-temperature
applications of Zr-Nb system through ternary alloying. Calculations were carried out
using the ab initio DFT employing the plane-wave pseudopotential method as
implemented within the CASTEP code. The influence of partial substitution for Nb
concentration with either Co or Sn concentrations was investigated on the Zr-Nb-X
systems of various concentrations. The resulting equilibrium lattice parameters,
heats of formation, elastic properties, and the density of states were evaluated to
mimic their structural, thermodynamic and mechanical stability trends.
The lattice parameters of binary systems Zr99Nb1.0, Zr98.8Nb1.2, Zr98.1Nb1.9, Zr97.5Nb2.5,
Zr97Nb3, Zr78Nb22, Zr78Nb22 and Zr50Nb50 gave better agreement with available
experimental data to within 5 %, while those for ternary systems have shown a
decrease with the introduction of the third element i.e. Co or Sn. The heats of
formation were negative (stable) at smaller concentrations of ≤ 1 at. % Co.
Moreover, the correlation of electronic stability using the DOS and the ∆Hf
calculations has indicated that the systems are thermodynamically stable within ≤ 1
at. % Co for (Zr99Nb1-xCox, Zr98.8Nb1.2-xCox, Zr98.1Nb1.9Cox, Zr97.5Nb1.5-xCox, Zr97Nb3-
xCox and Zr78Nb22-xCox) systems. It was found that the increase in Co concentration
enhances the thermodynamic, elastic and mechanical stability of the systems and
they are found to be stable at small concentrations of about 1 at. % Co.
Furthermore, the temperature dependence was carried out using Dmol3
. In
particular, the canonical ensemble (NVT) calculations were carried out at different
temperatures and we observed their structural behaviour with regard to the binding
energy and elastic properties at any given temperature up to 2400 K. We compare
the temperature dependence of Zr, Zr50Nb50, Zr78Nb22, Zr78Nb21Co1, Zr78Nb20Co2,
Zr78Nb19Co3, Zr50Nb49Sn1, Zr50Nb48Sn2 and Zr50Nb47Sn3 systems. In the case of
binary system, the Zr78Nb22 was more promising, showing lower binding energy of -
6.87eV/atom. It was shown that ternary additions with small atomic percentages of
Co and Sn have a significant impact on Zr-Nb alloy. Particularly, their elastic
properties showed a possible enhancement on the strength and ductility at high temperature. This was observed for 1 at. % since it satisfied the requirements for
ductility and strength as specified in literature. The Co and Sn addition on the
Zr78Nb22 system is more promising for high-temperature applications, with Sn being
more preferable. / National Research Foundation (NRF)
and Titanium Centre of Competence (TiCoC)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ul/oai:ulspace.ul.ac.za:10386/3827 |
| Date | January 2021 |
| Creators | Malebati, Magoja Martinus |
| Contributors | Chauke, H. R., Ngoepe, P. E. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xiv 115 leaves |
| Relation |
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