This project investigated the atomic-scale origins of strength and thermal stability in refractory high-entropy alloys (RHEAs), a class of materials considered promising for next-generation high-temperature applications such as aerospace components. A central focus was placed on local lattice distortion (LLD), a subtle structural feature arising from atomic size mismatch and chemical complexity, which is believed to play a key role in solid-solution strengthening and phase stability. Despite its importance, LLD has remained difficult to quantify experimentally, limiting its use in knowledge-based alloy design.
Neutron and synchrotron X-ray total scattering were used to simultaneously probe long-range crystallographic order and local atomic disorder. Pair distribution function (PDF) analysis in real space and Rietveld refinement in reciprocal space enabled quantitative determination of LLD. Molecular dynamics simulations were combined with variable-temperature neutron total scattering to separate static lattice distortions from thermal vibrations, supported by specific-heat analysis to estimate vibrational contributions. This integrated approach allowed direct tracking of LLD as a function of temperature across multiple RHEA compositions.
The results demonstrated that local lattice distortions in body-centred cubic RHEAs can be reliably quantified and, importantly, exhibit a clear temperature dependence—contrary to the long-standing assumption that LLD is temperature independent. This insight helps explain temperature-insensitive elastic properties observed in these alloys and provides a new framework for understanding their mechanical behaviour. The methodologies and findings established in this work offer a foundation for the rational design of more reliable, heat-resistant alloys for demanding industrial applications.