Fine-grained dual-phase high-entropy ceramics derived from boro/carbothermal reduction

Abstract

In the current work fine-grained dual-phase, high-entropy ceramics (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2-(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C with different phase ratios are prepared from powders synthesized via a boro/carbothermal reduction approach, by adjusting the content of B4C and C in the precursor powders. Phase compositions, densification, microstructure, and mechanical properties have been investigated. Due to the combination of pinning effect and the boro/carbothermal reduction approach, the average grain sizes (0.5–1.5 µm) of the dual-phase high-entropy ceramics, were much smaller as compared with previously reported values. The dual-phase high-entropy ceramics with 15 mol% boride phase exhibit the highest Vickers hardness (24.21 GPa) and fracture toughness (3.2 MPa•m1/2).

Highly wear resistant dual-phase (Ti-Zr-Nb-Hf-Ta)C/(Ti-Zr-Nb-Hf-Ta) B2 high-entropy ceramics

“…According to the XRD results [25], the investigated dual-phase HEC/HEB system consists of carbide and boride phases with lattice parameters a = 4.5413 Å for the FCC lattice of carbide and a = b = 3.1006 Å; c = 3.3670 Å for the hexagonal lattice of boride phases. These parameters slightly differ from the values measured for similar systems, which can be attributed to the difference in the HEC/HEB molar ratio and the difference in the concentration of transitional elements in carbide and boride phases in the investigated systems [16].…”

“…The grain sizes in the investigated dual-phase system are significantly smaller in comparison with the grain sizes (approximately 5–15 µm for systems with different compositions) reported for the first published system processed using a different processing route [16]. Publications, presenting the microstructure of dual-phase systems prepared with similar technology as the present study presenting similar grain sizes (approximately 0.5–2.7 µm) for carbide and boride phases as the present study [17,20].…”

“…Luo et al [16] recently developed fine-grained dual-phase, high-entropy ceramics (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B 2 – (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C with different phase rations using powders synthesised via boro/carbothermal reduction. High-density, homogeneously distributed DPHE-UHTCs, with different boride to carbide phase ratios, were prepared by SPS processing at 2000°C for 10 min under a 30 MPa applied load.…”

Low-temperature densification of high-entropy (Ti,Zr,Nb,Ta,Mo)C—Co composites with high hardness and high toughness

“…High-entropy transition metal carbide ceramics have been shown to possess high hardness, good elevatedtemperature flexural strength, low thermal conductivity, good high temperature wear resistance, and good oxidation resistance, and have attracted significant attention in recent years [1][2][3][4][5][6][7]. However, the sintering temperature of high-entropy carbide ceramics is typically ~2000-2300 ℃ [8][9][10], due to their primarily covalent bonding and low self-diffusion coefficients [11].…”

Quantitative inspection of grain‐scale chemical inhomogeneities in high‐entropy AlB2‐type transition metal diborides

“…Previous studies of HE borides have assumed that compositional homogenization was reached after synthesis/sintering, that metal distribution was random across all scales (i.e., from short to large scale range), and that the metallic species were present in ideal equimolar proportions 13–24 . Some authors acknowledged deviations from equimolar metal ratios but have stood by the assumption of overall long‐range chemical homogeneity 20–22,25 .…”