Structure and thermodynamic properties of a high-entropy TiZrNbHfTa alloy
Mechanical Properties of Metallic Materials and their Microstructural Origins
Final Report Abstract
The following bullet points summarize the most important scientific and non-scientific aspects of the project: The equiatomic fcc-FeNiCoCrMn, bcc-TiNbHfTaZr HEAs and their sub-alloys with less chemical complexity were prepared by arc-melting, cold-crucible casting and thermomechanical treatment in order to investigate phase stability, lattice strain and solid solution hardening behaviour. - The sub-alloys consisting of less number of constituent elements (fcc: equiatomic FeNiCoCr, FeNiCo, FeNi alloys and pure Ni / bcc: equiatomic TiNbHfTa, TiNbHf, TiNb alloys and pure Nb) were selected to be investigated in a comparison with the HEAs. - Quantitative determination of the structure formation especially with respect to the lattice distortion and the local atomic distribution in the bcc/fcc crystal lattice in both bulk and atomic scale was derived by performing (high-energy) x-ray diffraction study with the atomic pair distribution function (PDF) method and the Bragg peak broadening analysis. - All studied alloy samples formed single fcc or bcc solid solution phase and the thermal analysis revealed their thermal stability between 300 - 1500 K. - The micro lattice strain in the HEAs and their sub-alloys was quantified by Williamson-Hall methods on the Bragg intensities. The levels of micro lattice strain were not significantly different among the samples having different number of constituent elements. - To assess the lattice distortion present in the TiZrNbHfTa HEA, the local lattice strain has been studied through X-ray total scattering measurements, in comparison with four single phase bcc materials, with varying compositional complexity (Pure Nb, TiNb, TiNbHf and TiNbHfTa). - Significant PDF peak broadening was observed from multi component alloys ( n ≥ 3) indicating largely displaced atoms from their ideal lattice positions. - The TiZrNbHfTa and FeNiCoCrMn HEAs exhibited the broadest PDF peak, suggesting the highest level of local lattice strain. - PDF peak broadening and tensile yield strength did not exhibited a linear relationship with number of constituent n (compositional complexity and configurational entropy ΔSconf.). - The PDF peak width and yield strength appears to vary linearly with atom size misfit δr. - The lattice of fcc FeNiCoCrMn HEA is not anomalously distorted compared to an average fcc structure. - The evidence from this study suggests that the atomic size misfit is more important factor than the number of constituent elements in the determination of lattice distortion.
Publications
- Microstructure, mechanical and thermal oxidation behavior of AlNbTiZr high entropy alloy, Intermetallics 100, 9 (2018)
J Jayaraj, P Thirathipviwat, J Han, A Gebert
(See online at https://doi.org/10.1016/j.intermet.2018.05.015) - A comparison study of dislocation density, recrystallization and grain growth among nickel, FeNiCo ternary alloy and FeNiCoCrMn high entropy alloy, Journal of Alloys and Compound 790, 266 (2019)
P. Thirathipviwat, G. Song, J. Jayaraj, J. Bednarcik, H. Wendrock, T. Gemming, J. Freudenberger, K. Nielsch and J. Han
(See online at https://doi.org/10.1016/j.jallcom.2019.03.052)
