First hexagonal close packed high-entropy alloy with outstanding stability under extreme conditions and electrocatalytic activity for methanol oxidation

Abstract

Multi-component alloys containing 5 and 6 platinum group metals have been prepared by thermal decomposition of single-source precursors. It is the first successful example of high-entropy alloy preparation not requiring direct melting at high temperature or mechanical alloying, and can be further extended to other multicomponent metallic systems. Our single-source precursor strategy for the preparation of multicomponent alloys can be considered as a new approach in the design and optimization of refractory high-entropy alloys for a broad range of applications. Thermal decomposition occurs at low temperatures (below 800°C in H2 flow). The resulting hexagonal Ir0.19Os0.22Re0.21Rh0.20Ru0.19 alloy is the first example of a single-phase hexagonal high-entropy alloy. Heat treatment does not result in any phase changes up to 1500 K, which is a record temperature stability for a single-phase high-entropy alloy. Room temperature hydrostatic compression up to 45 GPa also highlights the system's stability as a single phase, with a bulk modulus smaller then individual platinum group metals (except Rh). The prepared alloys show pronounced electrocatalytic activity in methanol oxidation, which opens a route for the use of highentropy alloys as materials for sustainable energy conversion.

High-Entropy Alloys with Hexagonal Close-Packed Structure in Ir₂₆Mo₂₀Rh_22.5Ru₂₀W_11.5 and Ir_25.5Mo₂₀Rh₂₀Ru₂₅W_9.5 Alloys Designed by Sandwich Strategy for the Valence Electron Concentration of Constituent Elements in the Periodic Chart

“…The CrMnFeCoNi HEA with an hcp structure is unique, but it requires high pressure for its formation, i.e., it does not possess feature (3). Furthermore, a similar exception for feature (3) was reported by Yusenko et al 7) for the IrOs ReRhRu alloy comprising transition metals with near equiatomicity when it was produced as a HEA with a single phase by chemical reaction. The CrMnFeCoNi HEA with an hcp structure is composed of 3d transition metals only, and hence differs from the feature (4) as the Ir 26 Mo 20 Rh 22.5 Ru 20 W 11.5 and Ir 25.5 Mo 20 Rh 20 Ru 25 W 9.5 alloys consist of 4d or 5d transition metals.…”

“…As for the sample preparation, the present method, arc melting, is superior to the other methods as it is a conventional method and subsequently anneals at high temperature to homogenize only in the processing. In the other researches, the HEAs with hcp structure were prepared by applying high pressure 6) for alloys comprising 3d transition metals, mechanical alloying for light-weighted alloys, 5) and chemical reaction 7) for alloys consisting of transition metals. The present method exhibits an advantage over the other methods as one can produce enough amount of samples for performing researches at a laboratory scale.…”

Applications of High-Pressure Technology for High-Entropy Alloys: A Review

“…Pressure-induced polymorphic transitions (PIPT) to potentially disordered phase were observed. Yusenko et al [59] studied the temperature and pressure stability for a hcp Ir 0.19 Os 0.22 Re 0.21 Rh 0.20 Ru 0.19 HEA. The sample was loaded in a DAC cell and did not result in phase transition with a maximum pressure of 45 GPa.…”

Microstructure and Mechanical Properties of Sintered and Heat-Treated HfNbTaTiZr High Entropy Alloy

“…Numerous parameters were proposed by various authors in order to predict whether an alloy will exhibit a microstructure consisting of a solid solution with no intermetallic phases [1,[7][8][9][10]. The matrixes of high entropy alloys are typically bcc or fcc, but recently even HEAs with the hcp matrix have been reported [1,[11][12][13][14]. The HEAs with the bcc matrix usually exhibit high strength and lower plasticity whereas fcc HEAs have lower strength and high plasticity [1,6].…”