Instability-driven segregation of V group transition metals on HEB2 grain boundaries influencing enhanced mechanical properties
Abstract
Five metals share a common sublattice in the (Hf,Ta,Ti,Nb,Zr)B2 (HEB2). Most high-entropy materials are produced as polycrystalline materials in the form of sintered ceramics. The question of which metal species are located at grain boundaries is still unknown. Here, we calculated the grain-boundary energy γGB of four types of boundaries in five binary diborides and HEB2 using density functional theory (DFT). We analyzed the bonding at these boundaries using COHP and sampled cation segregation at six boundaries of HEB2, ordered and general, using Monte Carlo / molecular dynamics with a MACE potential that was fine-tuned for this system. According to our results γGB splits by group: the group V diborides NbB2 and TaB2 form boundaries with about half the energy of the group IV at three of the four types of GBs, ranging from 0.8 to 2.7 compared to 2.5--4.8~J/m2. COHP shows a significant difference at the Fermi level, namely the Me--B bonds of NbB2 and TaB2 are antibonding at Fermi energy (EF) in the bulk but bonding at the GB, while their integrated strength hardly changes. In HEB2 the segregation follows a similar pattern: Nb and Ta are enriched at five of the six grain boundaries, including general boundaries, up to 23--35~at.\% at 2000~K, although the size of the atoms would favor Zr and Hf in the expanded sites. A segregated Σ193 grain boundary can withstand 26 against 20~GPa for a random boundary in tension at 300~K. The grain boundaries of HEB2 are composed of group V metals, as suggested by the boundary energies of binaries compounds and their bonding at the Fermi level. Grain boundaries of the (Hf,Ta,Ti,Nb,Zr)B2 preferentially include Nb and Ta. This lowers the grain boundary energy and strengthens the boundaries. This consists of the lower boundary energy and changes Fermi level bonding in NbB2 and TaB2.
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BibTeX
@misc{alekseev2026instabilitydriven,
title = {{Instability-driven segregation of V group transition metals on HEB$_2$ grain boundaries influencing enhanced mechanical properties}},
author = {Daniil Alekseev and Viktor S. Baidyshev and Alexander G. Kvashnin},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.25295},
eprint = {2610.25295},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.25295},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Instability-driven segregation of V group transition metals on HEB_2 grain boundaries influencing enhanced mechanical properties
AU - Daniil Alekseev
AU - Viktor S. Baidyshev
AU - Alexander G. Kvashnin
PY - 2026
DA - 2026/10/18
PB - arXiv
DO - 10.48550/arxiv.2610.25295
UR - https://arxiv.org/abs/2610.25295
AB - Five metals share a common sublattice in the (Hf,Ta,Ti,Nb,Zr)B_2 (HEB_2). Most high-entropy materials are produced as polycrystalline materials in the form of sintered ceramics. The question of which metal species are located at grain boundaries is still unknown. Here, we calculated the grain-boundary energy γ_GB of four types of boundaries in five binary diborides and HEB_2 using density functional theory (DFT). We analyzed the bonding at these boundaries using COHP and sampled cation segregation at six boundaries of HEB_2, ordered and general, using Monte Carlo / molecular dynamics with a MACE potential that was fine-tuned for this system. According to our results γ_GB splits by group: the group V diborides NbB_2 and TaB_2 form boundaries with about half the energy of the group IV at three of the four types of GBs, ranging from 0.8 to 2.7 compared to 2.5--4.8~J/m^2. COHP shows a significant difference at the Fermi level, namely the Me--B bonds of NbB_2 and TaB_2 are antibonding at Fermi energy (E_F) in the bulk but bonding at the GB, while their integrated strength hardly changes. In HEB_2 the segregation follows a similar pattern: Nb and Ta are enriched at five of the six grain boundaries, including general boundaries, up to 23--35~at.\% at 2000~K, although the size of the atoms would favor Zr and Hf in the expanded sites. A segregated Σ193 grain boundary can withstand 26 against 20~GPa for a random boundary in tension at 300~K. The grain boundaries of HEB_2 are composed of group V metals, as suggested by the boundary energies of binaries compounds and their bonding at the Fermi level. Grain boundaries of the (Hf,Ta,Ti,Nb,Zr)B_2 preferentially include Nb and Ta. This lowers the grain boundary energy and strengthens the boundaries. This consists of the lower boundary energy and changes Fermi level bonding in NbB_2 and TaB_2.
ER -