Översikt
- Datum:Startar 29 januari 2026, 13:30Slutar 29 januari 2026, 16:00
- Plats:PJ-salen, Fysik Origo Building, Kemigården 1, Gothenburg
- Opponent:Dr. Matthew Tucker, Neutron Scattering Division, Oak Ridge National Laboratory, USA
- AvhandlingLäs avhandlingen (Öppnas i ny flik)
Refractory high-entropy alloys (RHEAs) are a novel class of alloys known for their exceptional mechanical properties at high temperatures, making them promising candidates for next-generation aerospace applications. RHEAs typically composed of multiple principal elements in (near-)equiatomic concentrations. A key factor contributing to their strength is local lattice distortion (LLD), which arises from atomic size mismatch, charge transfer effects and force constant variations among constituent elements. LLDs have been shown to contribute to solid solution strengthening and phase stabilisation, making them vital for mechanical performance and reliable processing of RHEAs. However, LLD remains poorly understood, particularly regarding quantification due to experimental challenges.
Neutron and synchrotron X-ray total scattering are the primary techniques used in this thesis, which enables simultaneous probing of both long-range order and local disorder. Quantitative determination of LLDs was done through small-box modelling of the pair distribution functions in real space, and through Rietveld refinement of diffraction patterns in reciprocal space. Molecular dynamics (MD) simulations provide the vibrational density of states (VDOS), allowing separation of scattering from dynamic (or thermal) and static atomic displacements. Specific heat measurements analysed using Debye approximation offer an alternative route for estimating thermal contributions.
It is shown that LLDs in bcc-structured RHEAs can be accurately quantified using both reciprocal- and real-space methods. A comprehensive methodology, combining variable-temperature neutron total scattering experiments with VDOS from MD simulations, revealed a negative temperature dependence of LLDs in a HfNbTaTiZr RHEA, which was further confirmed and extended to NbTaTiZr and MoNbTaW. Additional studies on alternative quantification methods and the effect of chemical heterogeneity establish a framework for understanding LLDs in RHEAs.
Neutron and synchrotron X-ray total scattering are the primary techniques used in this thesis, which enables simultaneous probing of both long-range order and local disorder. Quantitative determination of LLDs was done through small-box modelling of the pair distribution functions in real space, and through Rietveld refinement of diffraction patterns in reciprocal space. Molecular dynamics (MD) simulations provide the vibrational density of states (VDOS), allowing separation of scattering from dynamic (or thermal) and static atomic displacements. Specific heat measurements analysed using Debye approximation offer an alternative route for estimating thermal contributions.
It is shown that LLDs in bcc-structured RHEAs can be accurately quantified using both reciprocal- and real-space methods. A comprehensive methodology, combining variable-temperature neutron total scattering experiments with VDOS from MD simulations, revealed a negative temperature dependence of LLDs in a HfNbTaTiZr RHEA, which was further confirmed and extended to NbTaTiZr and MoNbTaW. Additional studies on alternative quantification methods and the effect of chemical heterogeneity establish a framework for understanding LLDs in RHEAs.
